THIS IS AN ORIGINAL MANUSCRIPT IT MAY NOT PB WITHOUT THE AUTHOR’S PERMISSION THE RELATION BETWEEN ROOT RESPIRATION AND ABSORPTION TEIS IS AN ORIGINAL MANUSCRIPT It MAY NOT BE COPIED WITHOUT THE AUTHOR’S PERMISSION Approved: Approved: Dean of (/he Graduate School. THE RELATION BETWEEN ROOT RESPIRATION AND ABSORPTION THIS AN ORIGINAL MA" . f IT MAY LOT BE COPIED THE AUTHOR’S PERMISSION THESIS Presented to the Faculty of the Graduate School of The University of Texas in Partial Fulfillment of the Requirements For the Degree of DOCTOR OF PHILOSOPHY By Leta Mae Henderson, 8.5., M.A. (Bisbee, Arizona) Austin, Texas June, 1932 335729 PREFACE This problem on root activities was undertaken under the direction of Dr. G.W.Goldsmith to whom the author wishes to express her indebtedness and deep appreciation for his kindly suggestions and helpful guidance throughout the course of the work. She also wishes to express her thanks to other workers in the associated fields of botany and physiology for construe tive and helpful suggestions. Leta Henderson TABLE OF CONTENTS Page Introduction 1 Materials and Methods 37 Computation of Results 43 Experimental Results 47 Discussion and Conclusions 114 Summary 125 Bibliography . 127 INTRODUCTION The endothermic processes taking place in the root supply the energy necessary for the various activities occurring there. Such endothermic processes are essentially oxidational, and under aerobic conditions which seem usual for mesophytes and xerophytes, result in the production of carbon dioxide as a characteristic end product. Not only is the production of carbon dioxide an indication of the liberation of energy but it also serves as a measure of the amount of energy so liberated since the heat of combustion of carbon is accurately known. The consumption of oxygen or the production of carbon dioxide thus furnish a quantitative measure of the energy relations of the root on which its activity must largely depend. In this sense resplrational values are measurements of vital activity. In the absence of definite knowledge concerning the internal transfer of energy, kinetic terms are employed. It has long been known that plant respiration may continue very slowly at low temperatures (Kostychev 1931). Since the work of Clausen (1890) and that of Matthaei (1904) a number of studies on the direct between respiration and temperature have been reported. According to Miller (1931), Clausen, working with germinating wheat, found temperature coefficients of respiration to be 2.86 between O°C and 10°C, and 1.09 between 30°C and 40°C with an average value between O°C and 40°C of 2.71. The results of Matthaei (1904), Blackman and Matthaei (1905) and Smith (1907) indicate that the temperature coefficient of plant respiration lies between 1 and 2, as would be expected in organic oxidations (Kostychev 1926). In this relation no optimum temperature appears; respiration increases in proportion to the temperature up to the injurious or lethal point for the tissues (Bonnier et Mangin 1884, Morse 1908, Burroughs 1922, Hopkins 1924 and others). Changing temperatures frequently show a markedly different effect on respiration than do constant temperatures. Muller Thurgau (1882) observed a marked increase in the respiration of potatoes stored at O°C when changed to a higher temperature as compared with those which had not been subjected to the lower temperature. Palladin (1899) found a similar relation in bean seedlings, and Burroughs (1922) with freshly picked apples. Kimbrough (1924) found the rate of respiration of potatoes to be inversely proportional to the storage temperature and directly proportional to the time of such storage. Hopkins (1924) observed in a range of temperatures from O°C to 11°C a minimum for the respiration of potato at 3°C. The horticultural practice of immersing plant parts in warm water depends for its success on this stimulatory effect (Kostychev 1926,1931). In respiratory studies on dormant apple seeds Harrington (1923) noted that the respiratory quotient increased with an increase in temperature, and that it decreased with a decrease in temperature. This seemed to indicate a storage of oxygen which became very considerable at 10°C and O°C. Cerighelli (1925) states that temperatures between 12°C and 24°C have no influence on the respiratory quotient. If there is complete oxidation of the respiratory materials the respiratory quotient remains constant (Kostychev). In succulents, however, this is not the case (Aubert 1892). At lower temperatures there is incomplete oxidation of carbohydrates and an excess of oxygen which serves in the formation of organic acids. An increase in water results in an increase of respiration up to a certain optimum. The respiration rate of air dried algae increased rapidly on the addition of water until the amount of water had reached 100 per cent. Not until a water content of 600 per cent had been reached was there a decrease in the rate of respiration, when gaseous exchange was apparently impaired (Fraymouth 1928). As plants dry out respiration decreases, with the result that in resting seeds with very little water content, respiration proceeds at a very low rate. The rate of respiration of wheat kernals is fairly constant up to 14.75 per cent moisture. Beyond this point there is a sharp rise so that an additional 1 per cent of moisture increases respiration nearly 200 per cent. A further moisture increase of 1 per cent accelerates respiration several hundred per cent (Bailey 1918). Barley kernals containing 10-11 per cent moisture liberated only 0.53 to 1.5 mg. of carbon dioxide per kilogram per hour. With 33 per cent moisture, 2000 mg. of carbon dioxide were liberated for the same period (Kolkwitz 1901). The intensity of respiration of air dried seeds of Acacia was only 0.0001 part of that of germinating seeds. Wheat seeds with a moisture content of 12 per cent had a respiration rate 0.03 that of active seedlings (White 1909). Similar observations have been made on various seeds by Bailey and Gurjar (1918), Bailey (1921), Duval (1904), Babcock (1912) and others. The effect of moisture on respiration varies with the different plant parts under consideration (Jacquot and Mayer 1927). The carbon dioxide production was found to increase up to the complete imbibition of bean seeds (117 per cent) and up to 58-60 per cent in plants. Sunlight has a stimulatory effect on respiration. Mayer and Deleano (1911) noted a daily periodicity in the intensity of respiration under natural, conditions. There are two theories to explain this stimulatory action; the first is that offered by Borodin (1876) who believes that in light, chlorophyll containing parts accumulate reserve respiratory materials which are used in respiration. This theory is strengthened by the work of Maximov (1902) who found that respiration of chlorophyll-free parts was essentially the same in light and in darkness. Spoehr (1915) has formulated the theory that autoxidation is initiated in the protoplasm due to the ionization of atmospheric oxygen in the sun’s rays. This has been shown to be probable by the work of Middleton (1927) who found that when the air passing over barley seedlings was artificially ionized by means of polarium, the rate of respiration was increased by as much as 29.1±5.6 per cent. The more oxygen there is present in the atmosphere the greater is the oxidation (Raber 1928),,since the amount of oxygen is connected with the ease in which it is taken up by the respiratory enzymes. De Saussure (1833) and Wilson (1885), however, found that reduction of the oxygen content to half, or even to 1 per cent had no retarding effect on respiration. Borodin (1874) found that in pure oxygen plants respire more vigorously but are soon exhausted by it. It has been shown that living wood parenchyma cells (Devaux 1899), roots (Stoklasa and Ernest 1909), and germinating seeds with compact swollen coats (Kostychev 1910) have an oxygen deficiency under normal conditions. There is probably a considerable oxygen deficiency in the interior of fleshy fruits, on account of which alsoholic fermentation is introduced as a normal process in fruits (Gerber 1896). Analysis of the hollow in pumpkin gave COg- 2.52 per cent and Og- 18.29 per cent (Devaux 1891). According to Miller (1931) the intensity of respiration in many plants is not markedly modified when the oxygen supply is reduced to one-half that normally present in the air, or when it is increased to 5-10 times that which normally occurs. The plant under consideration, as well as the conditions where the observation is made should be taken into account when studying the effects of the concentration of oxygen upon respiration. When the supply of oxygen in the air becomes less than 5-8 per cent, absorption of it is insufficient for most plants (Stitch 1891). If the oxygen supply is increased the plants may continue to respire normally for a period. In a few hours or days under a partial pressure increased 20-30 times, respiration declines and death ultimately ensues. Crocker and Davis (1914) have determined the oxygen concentration necessary for the development of different parts of the plant. The hypocotyl was capable of elongating 1.2 times its original length in the total absence of free oxygen. An air pressure of 5 mm. was necessary for greening and branching, while for the development of the primary root, a yet greater amount was necessary. An excess amount of carbon dioxide in the atmosphere surrounding plant tissues has a retarding effect on respiration. De Saussure noted that a 40 per cent content of carbon dioxide was injurious to plants. Most green plants in the presence of light, however, can tolerate considerable amounts of this gas. Bernard (1883) found that seed germination was entirely checked with a high content of carbon dioxide, but growth was resumed upon the restoration of the normal composition of the atmosphere. The respiratory quotient is not changed, even in the presence of 40 per cent carbon dioxide (Beherain et Maquenne 1886). The effect of the accumulation of carbon dioxide on respiration is more marked upon the process of aerobic respiration (Kidd 1916). Spoehr and McGee (1924) believe the effects of carbon dioxide on respiration are merely a temporary adjustment of the tissues. When the carbon dioxide content of the air surrounding a leaf was changed to a higher value the leaf showed a reduced emission of carbon dioxide for a period, but finally attained the same rate as before the change. When the carbon dioxide was reduced there was an increased rate in carbon dioxide output which was followed by a decrease to the original rate. Willaman and Beaumont (1928) exposed apple twigs, potato tubers, and wheat to high carbon dioxide concentrations. In all cases there was a decrease in the rate of respiration followed by immediate recovery when the carbon dioxide was removed. The respiratory rate then increased above the normal on account of the increased permeability of the protoplasm due to the action of the carbon dioxide on the proteins. Newcombe and Bowerman (1918) found that the accumulation of carbon dioxide in some cases had apparently no effect upon certain activities. Ventilation has no effect in producing better seedlings in the dark. This has no visible effect on the sensitive reactions of these plants to gravity and to light. The respiration of various flowers is higher than that in the leaves (De Saussure 1822), the maximum recorded being 24 times greater. The respiratory rate was greatest in the essential organs, especially at the time of opening of the flowers and at the time of fertilization. Bergman (1921, 1925) noted that flowers and tips of shoots were more seriously effected by a lack of oxygen than other parts, due to their high respiratory rates. The rate of respiration of 1 kg. of seeds is 1 co. of carbon dioxide in 24 hours with a water content of 10-11 per cent. An increase of water content to 33 per cent increases the carbon dioxide formation to 1200 cc. per kg. Garreau (1851) suggested that this might be a spontaneous autoxldation of various labile substances in the seed coats rather than true respiration. Kostychev (1881) states that the respiration of resting seeds is utterly unimportant. Mayer (1875) has shown that the grand curve for respiration of germinating seeds follows that of the grand period of growth during the same time. During the early days of germination the rate of respiration gradually increases, finally reaching a maximum and then decreasing again toward the end of germination. Benlakoff (1897) has shown that embryonic growing organs respire more vigorously than the endosperm. Kidd, West and Briggs (1921) and Hover and Gustafson (1926-27) show the rate of respiration decreases with advancing age of the plant. This difference in the respiratory rate of the different regions of the germinating seed has been further shown by Kolkwitz (1910) who divided wheat kernels transversely into equal portions. The embryo end respired 3 times as much carbon dioxide as the opposite end when equal weights of material were compared. The aerobic respiration of the embryj is 12 times that of the endosperm (Karcheviski 1903). Bailey and Gurjar (1920) also show a higher rate of respiration for the embryo than for the endosperm. Root respiration is essentially the same as that for the other organs of the plant. The source of oxygen necessary for root respiration may be internal as Cannon (1932) has recently shown. The solution surrounding the roots of various plants which were growing in sunlight increased as much as ten per cent in oxygen content. The greatest amount of oxygen was found in cultures where the temperature was highest. The explanation given for this is that the oxygen given off during photosynthesis is transported downward toward the roots and even to them. Since the rate of photosynthesis is greater at high temperatures, the amount of oxygen present in the solution is greater at these temperatures. Corn was peculiar in that the oxygen content of the solution was less when the plant was in light. The roots of these plants absorbed 14 per cent more oxygen than those which were on shaded plants. There are two explanations for this; the rate of respiration of roots in sunlight was high because of the higher temperature, or more rapid than the supply of internal oxygen. In any case internal oxygen plays an important part in aeration of plant tissues whether of root or shoot. Loweneck (1930) has also demonstrated the relationship between the root system and the aerial portions. He has further suggested that the photosynthetic activities of the green portions of the plant may result in the consumption of the respiratory carbon dioxide carried up by the transpirational stream, as well as the delivery of oxygen in the reverse direction. Michaels (1931) working with etiolated plants has shown the relationship of the aerial and root portions by changing the temperature around the roots. A change in either direction caused an increased respiratory rate of the shoot. Cerlghelli (1921) found that when the top remained attached the respiratory quotient of the roots in an artificial medium was less than 1. If the tops were removed, however, the respiratory quotient was 1. Active transpiration produced a significant increase in the amount of oxygen absorbed, and either a small decrease or increase in the amount of carbon dioxide given off. The transpiration stream probably removes some of the carbon dioxide in solution to the green parts of the plants, and also increases the oxygen in the returning sap stream. The author believes that absorption of water takes up the oxygen in solution and prevents the carbon dioxide from escaping. The latter is carried upward, thus setting up a gaseous current between roots and leaves. The aerial parts of the plants exert an influence on the gaseous exchange of the roots during strong transpiration.Cerighelli believes that wound effects on respiration are weak enough to be disregarded. In a second paper he divides roots into two classes depending on the respiratory quotient in the course of their development. In the first he places those roots which do not store up reserve material. The respiratory quotient here is never greater than 1; it is usually less. In the second are found roots of plants such as radish which accumulate a great deal of reserve material. In this case the respiratory quotient is greater than 1. A c change in temperature between 12°C and 24°C seems to have no effect on the respiratory quotient. Willaman and Brown (1930) point out three phenomena of plant respiration as measured by carbon dioxide output which might be explained on the basis of dissolved carbon dioxide. An increase in temperature results in a higher rate of carbon dioxide output which is temporary, and this temperature flush is caused by the lower solubility of carbon dioxide at higher temperatures. When tissues are stored in chambers in which carbon dioxide is allowed to accumulate and then if the carbon dioxide is swept out, there is a temporary rise in the rate of carbon dioxide output by the tissue. This may be due to an actual increase in respiration, since as Willaman and Beaumont (1928) have shown, the accumulation of carbon dioxide brings the proteins near the Isoelec trie point and hence increases the permeability and so the respiration, or it may be due to the diffusion of previously formed carbon dioxide which was held in solution because of the higher partial pressure of carbon dioxide in the atmosphere surrounding the tissue. There also seems to be a difference in the variety of tissue used, since twigs which possess the greatest winter hardiness show the lowest output of carbon dioxide. They also contain the lowest amount of dissolved carbon dioxide. Workers commonly assume the importance of root respiration to plant activities and plant life in general in supplying carbon dioxide to the soil, and do not examine the physiological relations of the process nor the ecological significance. Stoklasa and Ernest (1905) studied the respiration of the roots of various crop plants when grown im liquid cultures. During a period of 50 days at 15°C wheat roots gave off an average amount of 1.65 grams of carbon dioxide per 24 hours per gram of dried roots. Computed for 25 days the value was 2.54 grams. This agrees with the results obtained for sugar beet roots which gave off per 24 hours per gram weight of dried roots 0.217, 0.035, 0.0069, and 0.0026 grams of carbon dioxide as averages for periods of 25, 50, 75, and 120 days. The finer and younger the roots, the greater was the carbon dioxide output. The problem of the secretion of acids by roots has long been studied, and even yet there is no definite understanding of the matter. According to Haas (1916) Becquerel grew seedlings on litmus paper with the result that a permanent pink color was produced. He concluded that acetic acid was excreted by roots. Boussingault performed a similar experiment, and concluded that the acid excreted was lactic acid. Others left the nature of the acid undetermined, but concluded that there were other acid.s besides carbonic given off by roots. Czapek believed that certain cations were excreted as well. His list of substances given off by roots included potassium, calcium, magnesium, hydrochloric acid, sulphuric acid, and phosphoric acid. Stoklasa and Ernest, however, were unable to find either potassium or phosphoric acid in root excretions. Haas (1916) grew wheat and corn seedlings in culture solutions. After a period of from one to three weeks, he removed the plants and bubbled purified hydrogen gas thru the solution for about forty five minutes to expell all the carbon dioxide. At the end of that time the pH of the solution was the same as when the plants were first placed in them. He concluded from these results that carbonic acid was the only acid excreted by roots. Russell (1921) states that at one time it was supposed that special acids were excreted by plant roots to dissolve insoluble food materials in the soil. At the present time, so far as is known however, carbon dioxide is the only acid excreted. The evidence is of the negative kind and is not entirely satisfactory. The intensity of respiration may be measured in one of two ways; either by the amount of carbon dioxide produced, or by the amount of oxygen absorbed. The evolution of carbon dioxide and the consequent changes in the volume of a gas mixture of which this is a constituent has long been a favorite method employed in gas analysis. Where this method is applicable the simplicity and directness make it very desirable. With proper compensation for temperature and pressure, and with precautions against any differential solubility in water this method has been repeatedly shown to be capable of a high degree of accuracy. Results obtained by earlier workers made possible the Hempie apparatus for the laboratory analysis of comparatively large samples of gas. The portable apparatus of Haldane (1920) is also useful for this work. The obvious advantage of the portable apparatus, requiring only a small sample of gas has made it widely used in biological work, and has resulted in modifications necessary to meet the special requirements of various investigators. Thus the Carpenter burette is particularly favorable for the analysis of the atmosphere when highly accurate results are necessary and when the composition is not subject to too wide variations (Carpenter 1923). The Newcomer modification of the Haldane apparatus is recomended where a higher degree of accuracy than is possible with the original design is desirable. Many of these methods have been described by Dennis (1929). With a view to reducing the volume of the required sample and of maintaining in some degree the accuracy of the volumatric methods, several micro-methods have been designed. Krog (1920) has described a volumetric method of analysis which gives accurate readings to 0.001 per cent, while numerous workers have employed methods requiring but a fraction of a cubic centimeter sample (Schmidt-Jensen 1920 and Brown 1922). Volumetric methods for the measurement of carbon dioxide depend on the change in volume of the gas sample upon treatment with a solution of sodium hydroxide or potassium hydroxide. Volumes may be measured directly in a calibrated burette or indirectly by the use of the gas laws. Temperature is controlled, or the proper corrections are made for the observed changes. These corrections are automatically made in the Haldane apparatus and those similarly designed, by the proper balancing of pressure against that to which the original sample was exposed, the partial pressure of water vapor being maintained the same throughout the analysis. The above methods being very accurate and easy to perform, are highly desirable for the quantitative analysis of carbon dioxide when mixed with other gases. Roots when growing normally however, are not surrounded by a gaseous medium, but by one consisting of solid, liquid, and gas interphases, so that other methods have to be resorted to for the measurement of carbon dioxide given off by roots. One of the earlier volumetric methods for the measurement of carbon dioxide, and one which is still useful depends on the absorption of the gas in barium hydroxide of known concentration, and the estimation of the carbon dioxide by difference after titration with acid of known strength. The errors Involved in this method can be reduced to a minimum by the proper precautions to insure complete absorption of carbon dioxide by the hydroxide solution. To this end Pettinhoffer (1862) devised tubes set slanting and partly filled with baryta. Gas bubbled slowly through these tubes and traveled along their length through the solution, the speed of traveling being controlled by the angle of the tube. Mgny other absorption tubes have been designed, the purpose in all cases being to insure complete absorption and the minimum exposure to the air of the residual barium hydroxide during titration. Tashiro (1912) by the use of baryta was able to measure minute quantities of carbon dioxide by judging the amount of precipitate formed in single drops of the reagent. Partly because of the complications of this method it has not been extensively used. Spoehr (1923) used a solution of barium hydroxide and measured the electrical conductivity in order to obtain the concentration of the residual solution and so, by difference, of the carbon dioxide. The complications involved in these methods make them desirable only under conditions favorable for their application. Carbon dioxide measurements are frequently made gravimetrically by the determination of the weight of precipitate formed in a solution of barium hydroxide. This method is similar to but not as convenient as the volumetric method of Pettenkoffer, and hence is commonly used only when the requirements of the experiment favor it. After filtering, washing and drying, calculation from the equation for the formation of barium hydroxide shows that one gram of the latter is equivalent to 0.304 grams of carbon dioxide. Due to trouble of filtering and weighing this method is seldom employed. A more common gravimetric method frequently used by the earlier workers is absorption of carbon dioxide by soda lime, and observation of the consequent increase in weight. Descriptions of this direct method are given by Sachs (1859) and Pfeffer (1900). The gas circulated over the experimental plant was first freed of carbon dioxide by passage over soda lime. After circulation through the experimental chamber, the gas was dried over calcium chloride and finally treated in the soda lime tubes. The increase in weight of these was then observed. This method has dropped out of use at present not only because of the labor involved in weighing, but also because of the necessity of thorough drying and the difficulty of obtaining complete absorption in the soda lime tubes. Various types of apparatus have been devised for the determination of carbon dioxide in the air by the measurement of the thermal conductance. The principles Involved are discussed by Palmer and Weaver (1924) and also by Dennis (1929). By means of a resistance thermometer, which is also used as a heating coll, the rate of conductance through a chamber filled with the unknown gas mixture is compared to that in an identical chamber containing a gas of known conductance. The difference in temperature and hence the electrical resistance between the two thermometer resistance elements thus depends on the thermal conductance from the wire to the walls of the chambers. The thermal conductance of air is given by Dennis as 0.556 and that of carbon dioxide as 0.332, the ratio between the values being 0.585. The addition of one per cent carbon dioxide to a sample of air would thus make a reduction in thermal conductance of the mixture of 0.6 per cent. This method has been widely used for the determination of carbon dioxide in flue gases where the content of this gas is relatively high. It offers a simple means and also one which is readily made recording, but it is not sufficiently accurate for most work on plant respiration where carbon dioxide changes in the second decimal place are highly significant. One of the most satisfactory methods for measuring respiration is by means of changes in the pH of the solution due to the carbon dioxide given off by the organism. This has been used for respiration occuring in a gaseous as well as in a liquid medium. The carbon dioxide given off combines with water to form carbonic acid which changes the pH of the solution. This change in pH can be measured both colorimetrically and electrometrically. Many workers have devised respiratory chambers and employed the colorimetric method for determining the pH. The air surrounding the organism is mixed with the solution containing an appropriate indicator. The pH can be determined by means of a standard set of indicator buffer solutions, or by the various comparators or colorimeters. For organisms growing in liquid, samples to which the indicator is added may be withdrawn and the acidity determined. Proper precautions must be observed to prevent exposure and the consequent disturbance in the carbon dioxide content. The amount of carbon dioxide present can be calculated if the pH, the volume, and the buffer action of the solution are known. The respiratory rate of the organism can thus be determined. Electrometric methods, although capable of greater accuracy, are limited in use because of the complexity of the apparatus, secondary effects of substances present, and by the fact that the metallic electrode must be kept saturated with gaseous hydrogen. This method consists essentially in measuring the E.M.F. between electrodes placed in a known and an unknown concentration. Hydrogen electrodes can be used in both the solutions, or a calomel electrode can be used in the known concentration. The solution of known concentration is saturated with gaseous hydrogen at atmospheric pressure. Since the E.M.F. of one concentration is known, the electrode immersed therein is used as a reference, and in the equation for determining the pH this value is designated as 1. The equations for determining the pH are as follows (Clark 1928); V = Cn 0.00019H3T 10S C where V is the voltage, T the absolute temperature, On the known concentration and G the unknown. If the known concen# tration is designated as 1, the equation becomes: V ~ 1 0.0001983 T ~ 10g C ° r * V p H 0.0001983 T Although this method is frequently used for accurate determinations of hydrogen ion concentrations, it was not considered suitable for the purpose of the work to be described later because of the escape of carbon dioxide with the hydrogen necessarily bubbling through the solution. The quinhydrone electrode method for determining pH is another electrometric method which eliminates the error mentioned above. It is possible with this electrode to measure the pH in closed systems without bringing the solution in contact with the air. It is therefore very satisfactory for respirational work. In contrast to the hydrogen electrode method the solution is saturated with quinhydrone and requires no saturation with gases. Under these conditions the potential between the electrodes is definltly related to the hydrogen ion concentration of the solution. For the reference electrode a solution of known pH, commonly potassium acid phthalate saturated with quinhydrone, is used. This method has been the subject of frequent studies, the results and bibliography of which have been summarized by Clark. The equation for determining the pH from the E.M.F. is ; V K+ Y = 0.0001983 T where K is the pH of the solution of the reference electrode# Since this is a direct proportionality, a table can be made which converts E.M.F. into pH directly. For biological work the quinhydrone method offers the great advantage over that of the hydrogen electrode in that the carbon dioxide equilibrium is not disturbed by the sweeping action of hydrogen gas. It offers the further advantage of simplicity and ease of operation, in .that unblackened platinum electrodes may be used without complicated electrode vessels. Determinations are not accurate in strongly alkaline solutions, and salt errors are known to occur, but neither of these difficulties apply in resplrational work. Since the pH is the negative logarithm of the hydrogen ion concentration (H + ), and since Kendall has determined the dissociation constant (K) of carbonic acid for concentrations up to one atmosphere to be 3.5x10 , the amount of carbon dioxide in a solution may be determined from the pH, K, and the volume of solution used. (1) (H + ) = v where a is the degree of ionization and V is the number of liters of solution which contain one gram mole of carbon dioxide. If K is the ionization constant, the relationship of these two may be expressed: a 2 (2) K = —- (l-a)V In these two equations (H + ) and K are known, so the equations may be solved simultaneously and values for a and V determined for a certain pH. From (1) we obtain; (3) V= (F) Substituting this value for V in (2) we obtain; a 2 K = or, (1-a) & (H + ) K a ~ (H + )+K Solving for V in (3) K (4) V = p (H + ) +K(H + ) Using Kendall’s value for K, and the (H + ) corresponding to the observed pH, the molarity of the solution may be found from V in this way; 1 c = - V where 0 is the number of gram molecules per liter. The actual weight of carbon dioxide in grams per liter may then be calculated. Since the molecular weight of carbon dioxide is 44, the total weight of carbon dioxide present is 44C. If n represents the number of cc's of solution used, the weight of carbon dioxide in n cc’s is, 44Cn (5) Wt. = 1000 Since the volume of 1 gram of carbon dioxide at S.T.P. is 509 go’s, the volume of gas produced is 509x44Cn , , „ m x (6 Vol = (at S.T.P.) 1000 Thus it is only necessary to substitute values in equation (4) and (6) to obtain the amount of carbon dioxide. Root respiration may also be measured by estimating the amount of oxygen consumed. In carbon dioxide free atmosphere, oxygen may be determined by treatment with alkaline pyrogallol and observation of the change in volume. This is the method commonly employed in gas analyses (Dennis 1929, and Haldane 1912). When the oxygen is in solution, other methods are commonly used, avoiding the necessity of the laborious process of boiling off the gases preparatory to volumetric analysis. The standard method is that of Winkler (Standard Methods of Water Analysis 1923). This method depends on the oxidation of manganous hydroxide, formed by the addition of manganous sulphate and sodium hydroxide, to manganic hydroxide. Upon the addition of potassium iodide and hydrochloric acid, iodine is liberated. This is titrated with sodium thiosulphate of known concentration using starch as an indicator. From these reactions the amount of dissolved oxygen may be calculated, since the amount of sodium thiosulphate used is in direct proportion to the amount of oxygen. The formula given by Birge and Juday (1911) for calculating the amount of oxygen in cc’s per liter is, 0.055825nx1000 co per L = V 55.825 n V where n is the number of go's of N/100 thiosulphate solution, and V the capacity of the sample. This method has been used in measuring the respiration of aquatic organisms, and for this reason is very adaptable to measuring the respiration of roots. Indicator methods for the determination of the oxygen absorbed by respiring material have been described by Osterhout (1918). Manometric measurements of the oxygen absorbed have been used by Stich (1891) and others. The universal presence of water in active tissue necessitates absorption to satisfy the metabolic needs. In submerged plants this necessary water supply may be obtained by the various organs directly from the surrounding water. The water deficit in any tissue resulting from the use of water in growth or in chemical combinations, is not large. In most land plants with photosynthetic organs exposed in air, usually unsaturated with water vapor, an additional and com- paratively enormous amount of water must be supplied to equalize transpirational loss. Since the water deficit of the air is commonly much greater than that of active tissue, water is available only in the substrate. It is not surprising then, since tissues capable of absorbing water must have permeable cell walls which would also permit water loss, to find that leaves are of negligible importance in water absorption. Ganong (1894) found wilted leaves incapable of recovery when exposed to water or water vapor. Spalding (1906) found that while the leaves and twigs of various desert plants were capable of absorbing small amounts of water, this was insignificant compared to the amount lost in subsequent transpiration. Wetzel (1924) observed that if the cuticle of a leaf could be saturated with water the liquid could be absorbed, but in insignificantly small amounts. Wood (1925) observed that the leaves of the Australian Atriplex, when exposed to an atmosphere saturated with water vapor, carried on absorption. This ability to absorb water seemed to be correlated with the high salt content and hence the suction pressure of the leaves. It is clear that all significant water absorption in land plants takes place through the roots. The rate ef water absorption from the soil must be sufficient to supply both the transpirational and metabolic requirements. The metebolic requirements vary with the physiological activity of the plant tissues , those of transpiration with the evaporational conditions of the atmosphere. this variation being very wide under extreme conditions. This physiological balance in water relations is of the greatest ecological importance. Not only are the evaporatlonal conditions of the atmosphere and the physiological ones of the plant effective in this water equilibrium, but also the resistance of the soils to the withdrawal of water. This resistance is due to the surface forces of the soil particles and to the osmotic concentration of the soil solution. The adsorption of the water film to the surface of the soil grains and colloidal particles varies with the fineness of the soil and its colloidal content; the forces by which this adsorbed water is held vary inversely with the water content of the soil. The osmotic forces of the soil are due to the molecular and ionic condition of the solutes in the soil solution, and hence, at least indirectly, to the chemical nature of the compounds present. Various theories have been developed to explain the nature of the absorption of water from the soils. These may be grouped under three headings according to the forces assumed to be active in the process; imbibitional, osmotic and evaporational. Since the explanation of Sachs (1887) of the ascent of liquids in plants by imbibitional forces, various workers have attributed water absorption of the root to these forces. According to this explanation the saturation deficit in any part of the plant would be transferred through the adjacent tissues to the place where the minimum exists; this would be the roots since only here can the saturation deficit be reduced by absorption from the soil. From the work of Shull (1924) and others it is well known that imbibitional forces are of ample intensity, at least in seeds, for absorption of water even under extreme conditions, values as high as 1000 atmospheres being observed. He points out that the conditions for imbibitional absorption of soil water are favorable because of the hydrophyllic colloidal nature of the root hair walls and their direct contact with the water film around the soil particles. Shull agrees with Kunkel (1912) in that water may be transferred through the tissues imbibitionally in the direction of increasing saturation deficit. To many workers imbibition seems inadequate to account for the rate of water absorption from the soil by the roots since the imbibitional paths through a tissue would consist of the cytoplasm and cell walls and hence would be both restricted and devious, the cell sap being functional only in the maintenence of turgidity, i.e. contact between cytoplasm and wall. This theory also fails to explain the passage of water across the Casparian strip which is impermeable to water. Most workers regard osmotic forces as the most effective in the absorption of water. Osmotic activity postulates the activity of the cell sap as well as that of the cytoplasm and cell wall. Since the importance of osmotic action, pointed out by Dutrochet in 1837, many investigators have busied themselves with a possible mechanism which, in simple form, should be a gradient of osmotic concentration from the soil solution to the xylem vessels, the cells being semi-permeable. These assumptions are capable of experimental verification and have been the objective of various work to be discussed later. The mechanism of root exudation has remained inexplicable on the basis of either imbibitional or osmotic action. Pfeffer (1877) early recognized this difficulty in the assumed osmotic mechanism of absorption and suggested that exudation pressure may be due to unequal osmotic pressures in different parts of the plasma membrane, unequal distribution of osmotically active materials in the cell, or the presence of hypertonic solutions in the cell wall outside the plasma membrane. Lepeschkin (1906) assumed the first postulate in order to explain exudation by hydathodes of Phaseolus and the sporangio phores of Pilobolus. Blackman (1921) has discussed the weakness of such assumptions. The osmotic value of the cell sap of the epidermis is always higher than that of the surrounding soil solution. The force available for absorption is the difference between the osmotic value of the cell sap and the external solution less the turgor pressure of the cell wall (Thoday 1918). The conditions for the migration of water by osmotic action are fulfilled if there is an increasing gradient of absorbing power from cell to cell across the cortex to the fibro-vascular bundle. Ursprung has shown that there Is a gradient across the cortex to the endodermis and then a decrease in it and in the wood parenchyma. Shull (1924) has shown that the forces of imbibition and of osmosis tend to equilibrium. A saturation deficit in any part of a cell sets up a series of deficits in the other cells through the cell walls, the protoplasm, and the cell sap. A difference in osmotic pressure is thus set up between two cells. These two forces might explain the absorption and transfer of water across the cortex to the endodermis, but when the water reaches this region other forces must be used to explain the passage across the endodermis to the xylem vessels, since the osmotic pressure in these tissues is lower than that of the neighboring cortical cells. Many attempts have been made to explain this phenomenon as well as root ©r exudation pressure. Priestley (1920) suggests that the explanation put forward by Lepesohkin might be used to account for the passage of water from the living cells into the dead wood elements. This investigator believes free diffusion can explain the passage of water across the cortex, but at the endodermis further diffusion is checked due to the impermeable nature of the Casparian strip. The endodermis thus becomes the functional absorbing surface of the root (Priestley 1921). Atkins (1916) suggests that the cortical cells act as a semi-permeable membrane through which the xylem sap acts osmotically in causing a flow of water from the soil to the vessels, the resulting hydrostatic pressure giving rise to the phenomenon of root or exudation pressure. In all of these theories the cells of the endodermis have an active part in absorption. The transfer of water seems to be due to the action of the protoplasm of the cells. The process might be secretory or excretory as in animal tissue, utilizing respiratory energy (Miller 1931). No direct evidence has been obtained to show a correlation between these two processes except in the work of Newton (1924) who showed that under field conditions the plants gave off a greater amount of carbon dioiide when they were transpiring rapidly. This relationship is also suggested by the work of Livingston and Free (1917) who found that absorption was checked when the oxygen supply was limited. In order to bring about absorption from a more concentrated to a less concentrated solution, osmotic work has to be done, and in order to comply with the laws of thermodynamics, energy is required for the process. This energy might well be supplied by the respiratory activities of the tissues. Electro-endosmose might explain the movement of water across the endodermis providing there is a difference in the electrical charges on the two sides of the layer, and that a charge is on the solution passing through. That such a difference in potential exists has never been demonstrated, and even if such differences did exist their magnitude would be quite small and their influence on the movement of materials would be correspondingly small. Dixon (1909) and Renner (1912) believe absorption of water to be purely passive. The entrance of water into the root is due to forces exterior to it according to these workers. A saturation deficit is set up in the leaves due to transpiration. A tension is developed which is transmitted to the root and has the ultimate effect of partly drying it. The passage of water from the soil into the root is thus purely passive; the root acts as a filter. It is not necessary for root pressure to function according to this theory, and the importance of osmotic forces in the root under passive absorption is not known. The energy necessary to cause a saturation deficit in the leaves might come from one of two sources depending on the external conditions when transpiration is occurring. In an unsaturated atmosphere radient energy is sufficient to cause the evaporation of water from the surface of the leaves. In a saturated atmosphere, when evaporation forces no longer function, the energy might be supplied by the respiration of the leaves. Although no experimental work has been done to determine the exact relation between respiration and the loss of water in saturated atmospheres, Dixon has computed from results of others that respiration of the leaves could more than account for the transport of water through the stem and its loss to the air. It is to be noted that since the path of absorption from the soil to the xylem vessels lies along a radius, the area of conduction would decrease as the xylem is approached. The rate of movement of liquids would thus be at a maximum in the vascular cylinder, and the consequent osmotic difference would be at a maximum. The forces of imbibition, osmosis and passive absorption are all concerned in the intake of water by a root and its move ment across it. These may act separately or in combination, but even with a combination of all three it is doubtful whether they could supply enough water to make up for that lost by transpiration. As Overton (1921) says: ’’Little is actually known about the forces operating in the passage of water from the soil through the root into the vessels in sufficient quantity to supply the transpirational needs”. Blackman (1921) has summarized the situation thus: ’’Much more knowledge of cell dynamics is required before we can deal satisfactorily with such difficult problems as exudation and root pressure”. Explanations of mineral absorption may be placed in two classes. According to the theory of physical absorption the entrance of any solute into the vacuole is a ,process of diffusion from the higher concentration in the soil to the lower concentration in the cell sap. If the solute is being removed from the cell sap by adsorption to the colloids, precipitation, or chemical combination, equilibrium is not attained and the process may be continuous. Breazeale (1923) has formulated the hypothesis that a deficit of any particular element in any tissue will be transmitted to the absorbing surface by the removal and addition of ions to adjacent oppositely charged ions. The necessary element is removed from the soil solution in the same manner. In this way it is not necessary for an element to be transported from the soil directly to the tissue where it is needed, but results from ionic transfer in short steps. The physiological theories of mineral absorption have been formulated to explain the fact that in uncontaminated sap, concentration of solutes is frequently greater than that of the external solution. Lapique (1925) believes the ability oi a cell to accumulate salts in greater concentration than that of the surroundings is due to a ’’vital force” which he terms "epictesis”. The protoplasm, by rotation, is brought alternately in contact with the cell sap which is acid and the external solution which is alkaline or neutral. lons are absorb, ed from the soil and given off to the cell sap. The isoelectric point of the protoplasm determines its permeability and if the external solution is acid or alkaline, the change in permeability will determine what substances will be absorbed. The operation of Donnan equilibria has been suggested by some workers, but Briggs and Petrie (1928) have shown that these could not result in the ratio of the concentrations of internal to external solutions which occur in plants. The cell must do osmotic work in absorbing ions from a weaker to a stronger solution, such as occurs in secretion in animal glands. Just how this process is brought about is not known, but the ultimate source of energy must be respirationq.l. Of the early work done on water absorption by plants, that of Sachs is perhaps the best known. He noticed that potted plants wilted quite rapidly if the pots were surrounded with ice. Since his time many quantitative methods have been devised to measure the absorption of water. One of the most common and accurate methods is the determination of the loss in weight of the plant. This is measured by the intermittent weighing of a plant in an air tight container. The transpiration loss is considered absorption on the assumption that the water content of the plant is constant. While this method does not take into account loss or gain by the plant due to metabolic processes, this error is known to be small (two parts in a thousand). The most generally used method of measuring absorption directly is by means of a potometer. This consists essentially of a container with a tightly fitted stopper through which the plant is inserted. A graduated horizontal tube with an open end leads to the container. The whole apparatus is filled with water and placed in surroundings which have a constant temperature. As the water is absorbed by the roots, the water travels along the horizontal tube, permitting the rate of absorption to be easily measured. Many variations have been made from this simple method, but the principles are the same in all of them. Some methods combine the above method with the indirect one of weighing. The potometer is attached to the plant so that weighing is facilitated. This method is useful in comparing the rates of absorption and of transpiration. Newton (1924) devised a method for measuring absorption which is different from any of the above. The principle of this method is replacement. The plants were placed in sand cultures in quart jars which had a hole bored in the bottom. The sand was saturated, and when drainage had ceased, the jar was sealed. When the experimental interval was over, the amount of water necessary to add to the soil to again cause drainage was measured and used as a measure of the amount absorbed by the roots. MATERIALS AND METHODS To reduce individual variations as far as possible, seed from a pure strain of corn (Funk’s hybrid No. 517 - yellow dent) was used in all the experiments. This seed was obtained from Funk Bros. Seed Co., Bloomington, 111. Corn seemed best suited to the work and was therefore selected. The seeds were soaked overnight in water and then transferred to four per cent formalin for ten minutes. They were washed off with sterile water and placed in sterile Petri dishes containing a piece of filter paper, and to which a few cubic centimeters of sterile culture solution had been added. This method of sterilization seemed to be superior to washing the seeds with formalin. The overnight soaking allowed some of the more resistant spores to germinate so that they could be more easily killed. This treatment had no apparent injurious effects on germination. The seeds were allowed to germinate in the Petri dishes until the radicles were from one to two centimeters long. They were planted on perforated sheets of cork which were floated in dishes of culture solution. The solution was replaced at intervals of three to five days and was continuously aerated. The corn plants were kept in the laboratory at full daylight illumunation and grown in these culture dishes one or two weeks until they were needed. Knop’s solution was found to be satisfactory for growth of corn plants under these conditions. This medium contains per liter of distilled water; Ca'(N0 3 ) 2 1.00 gm. MgSO 4 0.25 ” KH 2 P0 4 0.25 " KNO~ 0.25 ” A few drops of ferric citrate solution supplied the necessary and available iron. The first sixteen experiments were carried out by means of the apparatus shown in figure 1. When the plants were about ten inches in height, they were placed in the experimental chamber A. A pyrex test tube about five inches in height and with a capacity of about ninety cubic centimeters was used. A rubber stopper was fitted with an inlet tube B leading from a flask 0, which in turn led from a large bottle of culture solution. An outlet tube D was led from the test tube to a three way stop cock E. A section was cut from the cork in order that the plant might be placed in the test tube easily and without injury. When the sector was in place the plant was held tightly in the stopper., but without undue pressure on the stem. A small pipette F with a rubber bulb was also fitted in the stopper. This was used to stir the solution before and after each reading. One opening G of the three way stop cock led to a horl- zontal piece of glass tubing of one millimeter bore, which was graduated and used as a potometer to measure the amount of solution absorbed by the roots during the experimental interval. The other opening H led to a quinhydrone electrode chamber I which was used in measuring the (H + ) and thus the carbon dioxide given off by the roots. Two glass tubes were fused into this chamber; one J was an opening through which a KOI bridge was inserted, the other was an outlet tube which led to a waste jar. The quinhydrone was inserted with the electrode which was a piece of colled platinum wire rather then platinum foil. A short piece of rubber tubing was inserted around both the electrode and the bridge so that the solution was not freely exposed to the air during the time of reading. The plant was covered with a lamp chimney M through which air of two humidities circulated, entering under a constant pressure at the top and escaping at the bottom. To obtain moist air, it was bubbled through three towers containing water and glass wool to break up the bubbles. The dry air was supplied in the same manner as that for moist air except that the air was bubbled through two calcium chloride towers. The entire apparatus was placed in a thermostat which maintained a temperature of 25°C. The room temperature varied from 20°C to 25°C. During a single experiment, however, it seldom varied more than two degrees. Readings were taken at hourly intervals for from six to fifteen hours. Since the rate of absorption is largely influenced by transpiration, the latter was changed by passing either moist or dry air over the leaves. Thus the rate of absorption could be changed, and the effect on root respiration studied. Preliminary experi ments were carried out to determine any abnormal behavior of the plants due to distilled water. To check this, plants were observed in rain water and in distilled water through which air had been bubbled for twelve hours. No difference in behavior of the plants could be observed. Measurements were thus taken using both distilled water and the culture solution. The change from the cultures to the tubes and solutions to be used in the experiment was made ten hours before readings were begun to allow the plants time to recover from the shock of change and handling. Absorption was measured by determining the amount of solution which passed along the potometer during one hour. Respiration was determined in two ways; either by the amount of carbon dioxide given off, or by the amount of oxygen absorbed. The increasing acidity due to the accumulation of carbonic acid is measured less satisfactorily in a buffered than in an unbuffered solution. It was thus desirable to make determinations of changes in the acidity in water rather than in culture solution by the use of the quinhydrone electrode. installed as already described. It was possible by means of the apparatus to withdraw a ten cubic centimeter sample of the solution, and to determine its acidity without bringing it in contact with the air. The culture around the roots was entirely replaced after each reading with fresh solution. This was insured by passing fresh liquid (500 cc) through the culture tube until acidity determinations showed the constant and original value. All the distilled water used was freshly made in a block tin apparatus and collected for use only after possible surface impurities had been washed away. Storage vessels used were of pyrex glass. In order to measure root respiration in. a solution containing electrolytes, and avoid the errors which may be due to the buffer action of the salts, the micro-Winkler method for measuring the amount of dissolved oxygen was used. This is a modification of the original Winkler method which makes it possible to measure the amount of oxygen in ten cubic centimeter samples. Greater accuracy was obtained by making the sodium thiosulphate solution N/160 rather than N/40. This method was used either in conjunction with the elec trometric method of carbon dioxide measurement, or separately as a measure of respiration on the assumption of a constant respiratory quotient. The sample for analysis was withdrawn through the potometer into the collecting tube with minimum agitation and exposure to the air. A Thompson and Miller apparatus was used (Zimmerman 1930). This is shown attached to the potometer in figure 2. The reagents were added immediately from the attached burette tubes and titration was promptly carried out, using a micro-burette. At the end of each set of readings, the height of the plant, number of leaves, length of roots, and the dry weight of the roots were recorded. Figure 1. Figure 2. COMPUTATION OF RESULTS Since the readings obtained in every experiment were in terms of pH, or in cc ’ s of N/140 sodium thiosulphate, it was necessary to change these into cc’s of carbon dioxide or of oxygen. The equations given on pages 23 and 24 were used in computing either the weight or volume of carbon dioxide from the pH. Since only pure water was used any change in acidity was due only to carbon dioxide (Haas 1916). If the original pH was 6.86, and the pH after one hour was 6.537, the amount of carbon dioxide given off by the roots during this time may be found in the following manner: Using equation (4) page 23, V 3.5X10" 7 10 -13 " 72 +3.5x10 -7 xlo“®* 8 ® = 5.19x10* 6 From page 23, 1 c = - V = 1.92x10“ 7 Using equation (5) page 24, 44Cn Wt = 1000 Since n in all the experiments was 90 cc, this becomes, 44x1.92x10“ 7 x90 Wt = 1000 = 7.6032X10" 7 gm. Using equation (6) page 24 to change the weight to volume. Vol = 509xWt =.000038699 cc. In like manner the volume of carbon dioxide which corresponds to a pH of 6.537 is .00106325 cc. The difference between these two is the amount of carbon dioxide given off by the roots. In this case this would be .00067363 cc. A conversion table was made using all the different pH’s obtained, in order to simplify computation when the same pH was found several times. This table is given on page 45. In changing cc’s of sodium thiosulphate to cc’s of oxygen the formula given by Birge and Juday (1911) was used (page2s). , _ 55«825n cc's per L - V V in all the experiments was 9, and n was the number of cc’s of sodium thiosulphate used in titrating. Since the volume of solution around the roots was 90 cc, the final equation becomes; 90 x 55.825n cc per 90 cc = § pH cc’s COg 6.860 .00038962 6 • 826 .00042933 6.775 .00050068 6.741 .00051388 6.724 .00052729 6.690 .00065156 6.673 .00068753 6.656 .00072563 6.622 .00080082 6.639 .00076635 6.605 .00086693 6.571 .00095708 6.554 .00100923 6.537 .00106325 6.503 .00120112 6.486 .00127327 6.469 .00134846 6.452 .00143010 6.435 .00150771 6.418 .00161250 6.401 .00165206 6.384 .00181408 6.367 .00192816 6.350 .00204901 6.333 .00207813 6.316 .00231718 6.299 .00252298 6.282 .00264754 6.265 .00281186 6.248 .00297669 6.231 .00317141 6.214 .00338628 6.197 .00360477 6.180 .00384544 6.129 .00467628 6.112 .00499588 6.095 .00533802 Conversion Table for Changing pH to Cubic Centimeters of Carbon Dioxide. pH cc’s C0 2 6.Q78 .00570426 6.044 .00652362 6.010 .00746795 5.976 .00856647 5.925 .01053172 5.840 .01491605 5.789 .01849148 5.755 .02133757 5.721 .02464322 5.670 .03204868 5.585 .04777067 5.500 .06396230 5.449 .07971856 5.415 .08598944 5.581 .10799799 5.330 .13543287 5.306 .14165918 5.289 .16250089 5.272 .18499096 5.255 .18886547 5.221 .21576978 5.204 .22776732 5.170 .27687033 5.136 .32955694 5.119 .34406975 5.102 .37022671 5.085 .40694989 5.000 .59602475 4.915 .85418792 4.881 1.02192948 4.830 1.28872060 4.796 1.50368208 4.779 1.62702560 4.745 1.89974070 4.711 2.21720400 4.660 2.80144845 .00 .01 .02 .03 .04 .05 .06 .07 .08 .09 .0 .0000 .0085 .0169 .0254 .0338 .0423 .0508 .0582 .0677 .0761 .1 .0846 .0931 .1015 .1100 .1185 .1269 .1354 .1438 .1523 .1608 .2 .1692 .1777 .1862 .1946 .2031 .2116 .2200 .2285 .2369 .2454 .3 .2538 .2623 .2708 .2793 .2877 .2961 .3047 .3130 .3215 .3300 • 4 .3384 .3469 .3554 .3639 .3723 .3808 .3891 .3978 .4060 .4146 .5 .4230 .4315 .4400 .4485 .4557 .4653 .4739 .4823 .4909 .4991 Conversion Table for Changing Cubic Centimeters of N/160 Sodium Thiosulphate to Cubic Centimeters of Oxygen when the Sample is 9 cc’s and the Total Volume is 90 cc ! s. EXPERIMENTAL RESULTS Experiment No. 1. The results of Experiment 1 are given in the table and the rates of absorption of water and evolution of carbon dioxide have been graphed. It will be seen that while there is a general parallel between the respiration and absorption rates, under the variable laboratory conditions, the correlation is not exact. The low respiration rate of the seventh and eighth hours is not correlated with the high absorption rate during this period, and may be due to a periodic decline toward the approach of the night periods. Maximum light intensity was reached from the fourth to fifth hours, and this will be seen to correspond to the increase in absorption and respiration at this time. The curves show that when the rate of absorption was high, that of carbon dioxide evolution decreased. Thus during the first two hours of the experiment the rate of absorption remained 0.05 with respirational values falling toward 0.001. Later in the course of observations when the rate of absorption rose to 0.07, carbon dioxide evolution fell to 0.0006. These discrepencies may indicate a transpiration stream, although Cannon (1932) found corn to be exceptional in not transporting oxygen from tops to roots. Since the leaves were exposed to diffuse light, a gradient of carbonic acid concentration between leaf and root tissue would be expected. This experiment was carried out from 9:00 A.M. to 5:00 P.M. December 22, 1930. The roots were placed in rain water. The leaves were exposed to room atmosphere. The amount of water surrounding the roots was 90 cc’s. The plant was one week old. The plant was exposed to the variable diffuse light of the laboratory. During the time of the experiment in hours as abscissae, the curves show; point, rate of respiration; and point-triangle, rate of absorption of water. The ordinates on the left side of the graph represent the rate of respiration in cubic centimeters of carbon dioxide per hour. The ordinates on the right side of the graph represent the rate of absorption of water in cubic centimeters per hour. Absorption of Water and. Evolution of Carbon Dioxide by Corn Roots. Time hours Absorption co ’s per hr Observed PH Total 002 content of solution, cc CO evolved cc’s per hour. 6.401 .001652063 1 .050 6.248 .002976697 .001324634 6.401 .001652063 2 .050 6.265 .002811863 .001159800 6.401 .001652063 3 .030 6.265 .002811863 .001159800 6.401 .001652063 4 .020 6.316 .002317197 .000665116 6 © 401 .001652063 5 .035 6.180 .003845438 .002193375 6.401 .001652063 6 .050 6.180 .003845438 .002193375 6.401 .001652063 7 .070 6.316 . .002317179 .000665116 6.401 .001652063 8 .050 6.333 .002078125 .000426062 Experiment 1. Absorption of Water and Evolution of Carbon Dioxide by Corn Roots. Experiment No. 2. The results of Experiment 2 are given in the table and the rates of absorption of water and evolution of carbon dioxide have been graphed. Experiment 2 was carried out in the same manner as Experiment 1 except that atmospheric conditions in the laboratory were probably not exactly similar. It is evident that this plant showed a remarkably close correlation between the respiration and absorption rates, and that there was no departure from this except at the final period of observation. Any variable factors evidently influenced respiration and absorption in a similar direction and to a similar degree. Thus, the high absorption rate at the sth hour is closely paralleled by the respiration rate, and both rates fell at the 6th hour to lower values. High absorption and respiration values of the sth hour correspond to the time of maximum illumination in the laboratory. There is no evidence of removal of carbon dioxide from the roots in the transpiration stream as the curve of carbon dioxide evolution and water absorption remain essentially parallel. This experiment was carried out from 9:00 A.M. to 5;00 P.M. December 23, 1930. The roots were placed in rain water. The leaves were surrounded with air of room humidity. The amount of water surrounding the roots was 90 cc’s. The plant was one week old. The plant was exposed to the variable diffuse light of the laboratory. During the time of the experiment in hours as abscissae, the curves show; point, rate of respiration; and point-triangle, rate of absorption of water. The ordinates on the left side of the graph represent the rate of respiration in cubic centimeters of carbon dioxide per hour. The ordinates on the right side of the graph represent the rate of absorption of water in cubic centimeters per hour. Absorption of Water and Evolution of Carbon Dioxide by Corn Roots. Time hours Absorption cc ’s per hr Observed pH Total COg content of solution co COg evolved cc ’s per hour. 6.435 .00150771 1 .045 6.231 .00317141 .00166370 6.435 .00150771 2 .050 6.231 .00317141 .00166370 6.435 .00150771 5 .045 6.265 .00281186 .00130415 6.435 .00150771 ' ' " • J - > 4 • 040 6.265 .00281186 .00130415 * 6.435 .00150771 5 .075 6.197 .00360477 .00209706 6.435 .00150771 6 .040 6.265 .00281186 .00130415 6.435 .00150771 7 .055 6.265 .00281186 .00130415 6.435 .00150771 8 .055 6.214 .00338628 .00187857 Experiment 2. Absorption of Water and Evolution of Carbon Dioxide by Corn Roots. Experiment No. 3. The results of Experiment 3 are given in the table and the rates of absorption of water and evolution of carbon dioxide have been graphed. This experiment was carried out with an older plant than that used in experiments 1 and 2, and the observation period was somewhat greater. The plant was also kept under conditions of darkness and periodically dry and moist air. It will be seen that the high rate of absorption during the initial four hour exposure to dry atmosphere was not effective in altering the carbon dioxide evolution from the roots until two hours later, when the rate of respiration rose markedly. During the remainder of the experiment when the plant was kept in moist air, absorption and respiration rates correlated rather closely. It appears that during the initial four hour dry period to which the plants were suddenly subjected after the night conditions in the laboratory, there was either a markedly depressed respirational rate in the roots, or removal of part of the dissolved carbon dioxide with the transpirational stream. Since the tops were not exposed to light this transportation would only proceed to an equilibrium with the tissues outside of the root and would be undisturbed by photosynthetic activity. This experiment was carried out from 7:00 A.M. to 6;00 P.M. January 10, 1931. The roots were placed in rain water. The leaves were surrounded with dry air for four hours and then with moist air. The plant was 2 1/2 weeks old and 23 inches high, the length of the roots being 11 inches. During the time of the experiment in hours as abscissae, the curves show; point, rate of respiration; and point-triangle, rate of absorption of water. The ordinates on the left side of the graph represent the rate of respiration in cubuc centimeters of carbon dioxide per hour. The ordinates on the right side of the graph represent the rate of absorption of water in cubic centimeters per hour. Absorption of Water and Evolution of Carbon Dioxide by Corn Roots. Time hours Absorption co ’s per hr Observed pH Total COo content of solution, cc COg evolved, cc ’ s per hour. 6.180 .00384543 1 • 055 6.044 .00652361 .00267818 6.180 .00384543 2 .050 6.078 .00570426 .00185883 6.180 .00384543 3 .040 6.044 .00652361 .00267818 6.180 .00384543 4 .040 5.976 .00856647 .00472104 6ol80 .00384543 5 .010 6.044 .00652361 .00267818 6.180 .00384543 6 .007 6.078 .00570426 .00185883 6.180 .00384543 7 .005 6.010 .00746794 .00362251 6.180 .00384543 8 .000 6.078 .00570426 .00185883 6.180 .00384543 9 .015 6.010 .00746794 .00362251 6.180 .00384543 10 .020 6.010 .00746794 .00362251 6.180 .00384543 11 .020 6.010 .00746794 .00362251 Experiment 3. Absorption of Water and Evolution of Carbon Dioxide by Corn Roots. Experiment No. 4. This experiment was carried out simultaneously with Experiment 3 and duplicated it exactly except that the initial four hour period was carried out under conditions of moist air rather than dry, and the remainder of the experiment was carried out in dry air. This plant showed higher respiration and absorption values than that in Experiment 3. The respiration values are variable, although the general course of the two processes is similar. The low rate of absorption during the initial moist period is not paralleled by the rising respiration rate. During the remainder of the experimental period there was a general correlation between the rising rates of absorption and carbon dioxide evolution. It is apparent that in Experiments 3 and 4 the chief discrepencies between the absorption and respiration rates occur during the initial four hour period, irrespective of the humidity to which the plant was subjected. This may be related to the conditions preceding the experiment or to the rapid saturation of the tissues with carbon dioxide while the transpiration stream was low. The greater transpiration stream Induced by the exposure to dry air to which Experiment 3 was subjected, carried away from the root system sufficient carbon dioxide to produce a temporary depression in carbon dioxide until increased production balanced this loss. This experiment was carried out from 7;00 A.M. to 6:00 P.M. January 10, 1931. The roots were placed in rain water. The leaves were surrounded with moist air for four hours and then with dry air. The plant was 2 1/2 weeks old and 24 inches high, the length of the roots being 10 inches. During the time of the experiment in hours as abscissae, the curves show; point, rate of respiration; and point-triangle, rate of absorption of water. The ordinates on the left side of the graph represent the rate of respiration in cubuc centimeters of carbon dioxide per hour. The ordinates on the right side of the graph represent the rate of absorption of water in cubic centimeters per hour. Absorption of Water and Evolution of Carbon Dioxide by Corn Roots. Time hours Absorption co ! s per hr Observed pH Total COo content of solution, cc CO2 evolved, cc’s per hour. 1 .010 6.180 5.925 .00384543 .01053171 .00668628 2 .010 6.010 5.789 .00746794 .01849148 .01102354 3 .015 6.010 5,755 .00746784 .02133756 .01386962 4 .015 6.010 5.755 .00746784 .02133756 .01386962 5 .060 6o095 5.789 .00533801 .01849148 .01315346 6 .040 6.095 5.789 .00533801 .01849148 .01315346 7 .065 6.095 5.755 .00533801 .02133756 .01599954 8 .070 6.095 5.755 .00533801 .02133756 .01599954 9 .055 6.095 5.755 .00533801 .02133756 .01599954 10 .075 6.095 5.789 .00533801 .01849148 .01315346 11 .075 6.095 5.721 .00533801 .02464321 .01930580 Experiment 4. Absorption of Water and Evolution of Carbon Dioxide by Corn Roots. Experiment No. 5. Experiment 5 was carried out under the same conditions as Experiment 4 except that the initial exposure to moist air was three instead of four hours. The results are tabulated and those for the absorption of water and the evolution of carbon dioxide have been graphed. It will be seen that although both the rates of respiration and absorption are markedly lower than those exhibited by the plant in Experiment 4, they correlated rather closely throughout the ten hour course of the experiment. As in the preceding case the low absorption rate in the humid chamber was in contrast to a comparatively high rate of respiration. The respiratlonal values show that the roots of this plant reached a maximum rate of carbon dioxide evolution within an hour after exposure to dry air, and maintained this value until the end of the experiment, showing no variation coincident with that of the sth and 10th hours of absorption. This experiment was carried out from 7:00 A.M. to 5:00 P.M. January 16, 1931. The roots were surrounded with rain water. The leaves were placed in moist air for three hours and then in dry air. The plant was 2 1/2 weeks old and 21 inches high, the length of the roots being 9 inches. During the time of the experiment in hours as abscissae, the curves show; point, rate of respiration; and point-triangle, rate of absorption of water. The ordinates on the left side of the graph represent the rate of respiration in cubuc centimeters of carbon dioxide per hour. The ordinates on the right side of the graph represent the rate of absorption of water in cubuc centimeters per hour. Absorption of Water and Evolution of Carbon Dioxide by Corn Roots. Time hours Absorption cc’s per hr Observed pH Total C0 2 content of solution, cc COg Evolved cc’s per hour. 6.605 .00086692 1 .000 6.299 .00252297 .00165605 6.605 .00086692 • 2 .000 6.299 .00252297 .00165605 6.605 .00086692 5 .000 6.350 .00204901 .00118209 6.605 .00086692 4 .025 6.265 .00281186 .00194494 6.605 .00086692 5 .010 6.265 .00281186 .00194494 6.605 .00086692 6 .025 6.265 .00281186 .00194494 6.605 .00086692 7 .025 6.265 .00281186 .00194494 6.605 .00086692 8 .025 6.265 .00281186 .00194494 6.605 .00086692 9 .025 6.265 .00281186 .00194494 6.605 .00086692 10 .040 6.265 .00281186 .00194494 Experiment 5. Absorption of Water and Evolution of Carbon Dioxide by Corn Roots* Experiment No. 6. The results of this experiment have been tabulated and those for the evolution of carbon dioxide and the absorption of water have been graphed. The conditions of this experiment varied from those of experiment 3 in that the initial exposure to dry air was 8 instead of 4 hours. Throughout the fourteen hours duration of the experiment, the respiration and absorption curves show a fairly close correlation. A very high absorption rate occurred when the plant was first exposed to dry air, as in Experiment 3. This rapid rate of absorption quickly fell to a lower level, perhaps because of the effect of stomatai adjustment on transpiration. This high initial transpiration is not reflected in the rate of carbon dioxide evolution. The change from dry to moist air resulted in immediate depression of both the absorption and respiration rates, a movement which required three hours to reach its minimal level. It will be seen from these results that the absolute values of the rates of respiration and absorption are greater in Experiment 3 than in Experiment 6, but the values for Experiment 6 are but slightly below those obtained for the period of exposure to dry air in Experiment 5. Experiment 4, as already mentioned, showed very high rates for both absorption and carbon dioxide evolution. This experiment was carried out from 7:00 A.M. to 8:00 P.M. January 17, 1931. The roots were placed in rain water. The leaves were surrounded with dry air for eight hours and then with moist air. The plant was 2 1/2 weeks old. During the time of the experiment in hours as abscissae, the curves show; point, rate of respiration; and point-triangle, rate of absorption of water. The ordinates on the left side of the graph represent the rate ox respiration in cubuc centimeters of carbon dioxide per hour. The ordinates on the right side of the graph represent the rate of absorption of water in cubuc centimeters per hour. Absorption of Water and Evolution of Carbon Dioxide by Corn Roots. Time hours Absorption co ’s per hr Observed pH Total COo content of solution, cc COg evolved go’s per hour. 6.486 .00127327 1 • 035 6.350 .00204901 .00077574 6.486 .00127327 2 .010 6.350 .00204901 .00077574 6.486 .00127327 3 .010 6.316 .00231717 .00104390 6.486 .00127327 4 .025 6.299 .00252797 .00125470 6.486 .00127327 5 .020 6.333 .00207813 .00080486 6.486 .00127327 6 • 020 6.350 .00204901 .00077574 6.486 .00127327 7 .040 6.316 .00231717 .00104390 6.486 .00127327 8 • 020 6.350 .00204901 .00077574 6.486 .00127327 9 .020 6.350 .00204901 .00077574 6.486 .00127327 10 .005 6.401 .00165206 .00037879 6.486 .00127327 11 .005 6.384 .00181408 .00054081 6.486 .00127327 12 .005 6.384 .00181408 .00054081 Experiment 6. Absorption of Water and Evolution of Carbon Dioxide by Corn Roots. Experiment No. 7. The results of this experiment have been tabulated and those for respiration and absorption have been graphed. The conditions of Experiment 7 were identical with those of Experiment 6. Here again, although the curves for carbon dioxide evolution and water absorption are variable, they show a rather close correlation throughout the course of the experiment. During the initial eight hour dry period the high absorption rate of the first hour fell gradually through a variable course to one third this initial value, and then increased toward the maximum value. The transfer to moist air was followed, as in Experiment 6, by an absorption rate which gradually fell to a minimum. The rate of carbon dioxide evolution followed the general course of the rate of absorption closely, fluctuating during the initial eight hour dry period and gradually falling to a minimum during the final five hour exposure to moist air. In absolute values, the absorption rate of Experiment 7 was considerably higher than that in Experiment 6, and since the final minimum values were similar, fell more rapidly during the exposure to moist air. In contrast to this, the respiration rate of Experiment 7 showed similar values to that exhibited in Experiment 6. This experiment was carried out from 7joo A.M. to 8;00 P.M. January 17, 1931. The roots were placed in rain water. The leaves were surrounded with dry air for eight hours and then with moist air. The plant was 2 1/2 weeks old. During the time of the experiment in hours as abscissae, the curves show; point, rate of respiration; and point-triangle, rate of absorption of water. The ordinates on the left side of the graph represent the rate of respiration in cubic centimeters of carbon dioxide per hour. The ordinates on the right side of the graph represent the rate of absorption of water in chbic centimeters per hour. Absorption of Water and Evolution of Carbon Dioxide by Corn Roots- Time hours Absorption cc’s per hr Observed pH Total COg content of solution, cc COg evolved cc’s per hour. 6.486 .00127327 1 .100 6.299 .00252297 .00124970 6.486 .00127327 2 .065 6.350 .00204901 .00077574 6.486 .00127327 3 .090 6.316 .00231717 .00104390 6.486 .00127327 4 .050 6.350 .00204901 .00077574 6.486 .00127327 5 .050 6.316 .00231717 .00104390 6.486 .00127327 6 .030 6.316 .00231717 .00104390 6.486 .00127327 7 .040 6.316 .00231717 .00104390 6.486 .00127327 8 .075 6.282 .00264754 .00137425 6.486 .00127327 9 .050 6.350 .00204901 .00077574 6.486 .00127327 10 .040 6.350 .00204901 .00077574 6.486 .00127327 11 .015 6.350 .00204901 .00077574 6.486 .00127327 12 .010 6.384 .00181407 .00054086 6.486 .00127327 13 .000 6.384 .00181407 .00054086 Experiment 7. Absorption of Water and Evolution of Carbon Dioxide by Corn Roots. Experiment No. 8. The results of this experiment have been tabulated and those for respiration and absorption have been graphed. This experiment was carried out with an initial exposui*e to moist conditions for a period of four hours, followed by eleven hours exposure to dry air. It will be seen ±rom the results that this plant showed a remarkably close correlation between the rates of respiration and of water absorption, the two curves paralleling each other closely to the end of the experiment. The rate of absorption fell abruptly from the initial maximum value to a minimum which was maintained throughout the period of exposure to moist air, and continued at this level for two hours following the subjection to the dry atmosphere. After the six hour period the rate rose quickly to a high level which was maintained until the final three hours of the experiment, during which the rate declined. The respiration rates followed the same order of change but the degree of change was less. The absolute values of absorption were similar to those exhibited in Experiment 6, but the respiration values during this time were considerably below those of Experiment 6, and more like those of Experiment 5. An explanation for delay in transpiration and respiration response following the change to dry air is not apparent. The fact remains, however, that both activities showed a parallel and simultaneous variation. This experiment was carried, out from 7;00 A.M. to 10:00 P.M. January 30, 1931. The roots were placed, in rain water. The leaves were surrounded, with moist air for four hours and then with dry air. The plant was two weeks old. During the time of the experiment in hours as abscissae, the curves show; point, rate of respiration; and point-triangle, rate of absorption of water. The ordinates on the left side of the graph represent the rate of respiration in cubic centimeters of carbon dioxide per hour. The ordinates on the right side of the graph represent the rate of absorption of water in cubic centimeters per hour. Absorption of Water and Evolution of Carbon Dioxide by Corn Roots. Time hours Absorption co *s per hr Observed Total COp COg evolved go's per hour. PH content of solution, co 6.860 .00038962 1 .025 6.537 .00106325 .00067363 6.860 .00038962 2 .000 6.724 .00052729 .00013767 6.860 .00038962 3 .000 6.724 .00052729 .00013767 6.860 .00038962 4 .000 6.742 .00052729 .00013767 6.860 .00038962 * 5 .000 6.742 .00052729 ..00013767 6.860 .00038962 6 .000 6.742 .00052729 .00013767 6.860 .00038962 7 .020 6.690 .00065155 .00026193 6.860 .00038962 8 .020 6.690 .00065155 .00026193 6.860 .00038962 9 .020 6.690 .00065155 .00026193 6.860 .00038962 10 .020 6.690 .00065155 .00026193 6.860 .00038962 11 .020 6.690 .00065155 .00026193 6.860 .00038962 12 .020 6.690 .00065155 .00026193 6.860 .00038962 13 .015 6.690 .00065155 .00026193 6.860 .00038962 14 .015 6.724 .00052729 .00013767 6.860 .00038962 * . 15 .010 6.742 .00052729 .00013767 Experiment 8. Absorption of Water and Evolution of Carbon Dioxide by Corn Roots. Experiment No. 9. This experiment was carried out under identical conditions with Experiment 8, and simultaneously with it. In this case the general parallel between the rates of absorption and respira tion is not as close as in the preceding. From the initial high absorption value the rates fell to a minimum from which they quickly increased to high and variable values upon exposure to dry air. The rates of respiration fell during the initial four hour period paralleling the absorption curve, but maintained this minimum value during the dry period with but a single significant variation. The absolute values of absorption during the dry period were similar to those of Experiments 4 and 7• The rate of carbon dioxide evolution remained at a general value similar to that shown during the moist period in Experiment 3 and 8. The low respiration values in this case may be provisionally explained by a transportation of carbon dioxide in the transpiration stream. This experiment was carried out from 7:00 A.M. to 10:00 P.M. January 30, 1931. The roots were placed in rain water. The leaves were surrounded with moist air for four hours and then with dry air. The plant was two weeks old. During the time of the experiment in hours as abscissae, the curves show; point, rate of respiration; and point-triangle, rate of absorption of water. The ordinates on the right side of the graph represent the rate of absorption of water in cubic centimeters per hour. The ordinates on the left side of the graph represent the rate of respiration in cubic centimeters of carbon dioxide per hour. Absorption of Water and Evolution of Carbon Dioxide by Corn Roots. Time hours Absorption co’s per hr Observed pH Total COg content of solution, cc COg evolved cc’s per hour. 6.860 .00038962 * 1 .080 6.622 .00080081 .00041119 6.860 .00038962 2 • 040 6.673 .00068753 .00029751 6.860 .00038962 3 .020 6.724 .00052729 .00013767 6.860 .00038962 4 • 020 6.724 .00052729 .00013767 6.860 .00038962 5 .090 6.724 .00052729 .00013767 6.860 .00038962 6 .080 6.724 .00052729 .00013767 6.860 .00038962 7 .095 6.724 .00052729 .00013767 6.860 .00038962 8 .080 6.724 .00052729 .00013767 * 6.860 .00038962 9 .070 6.724 .00052729 .00013767 6.860 .00038962 10 .100 6.690 .00065155 .00026193 6.860 .00038962 11 • 070 6.724 .00052729 .00013767 6.860 .00038962 12 .100 6.724 .00052729 .00013767 6.860 .00038962 13 .070 6.741 .00051387 .00012425 6.860 .00052729 14 .065 6.741 .00051387 .00012425 6.860 .00052729 15 .065 6.741 .00051387 .00012425 Experiment 9. Absorption of Water and Evolution of Carbon Dioxide by Corn Roots. Experiment No. 10. The results of this experiment are given in the table and the values for the evolution of carbon dioxide and the absorption of water have been graphed. This experiment was carried out with somewhat younger plants than those previously employed. During the initial three hour period moist air circulated around the leaves, and during the remainder of the experiment dry conditions were maintained. The general correlation between the respiration and absorption curves is close. The rates of absorption remained moderately low during the period of exposure to moist air and for the hour following the transfer to dry atmosphere. It then rose sharply to maximum values which were not maintained but fell during the final two hours of observation to the original low value. From a high Initial rate of respiration the values showed a general decrease during the course of the experiment, exhibiting during this fall, reactions paralleling those of absorption. The absolute values of absorption are in the range of those observed in Experiments 4 and 7, and those of respiration in Experiments 6 and 7. This experiment was carried out from 7:00 A.M. to 3:00 P.M. February 1, 1931. The roots were placed in rain water. The leaves were surrounded with moist air for three hours and then with dry air. The plant was 1 1/2 weeks old and 12 inches high, the length of the roots being 4 inches. During the time of the experiment in hours as abscissae, the curves show; point, rate of respiration; and point-triangle, rate of absorption of water. The ordinates on the right side of the graph represent the rate of absorption of water in cubic centimeters per hour. The ordinates on the left side of the graph represent the rate of respiration in cubic centimeters of carbon dioxide per hour. Absorption of Water and Evolution of Carbon Dioxide by Corn Roots* Time hours Absorption co ’ s per hr Observed PH Total COg content of solution, cc COg evolved cc ’s per hour. 6.860 .00038962 1 • 025 6.435 .00150771 .00111809 6.826 .00042933 2 • 040 6.520 .00113339 .00070406 6.775 .00050068 3 .045 6.469 .00134846 .00084777 6.775 .00050068 4 .040 6.520 .00113339 .00063271 6.775 .00050068 5 .075 6.486 .00127327 .00077258 6.775 .00050068 6 .075 6.503 .00120112 .00070043 6.775 .00050068 7 .040 6.554 .00100923 .00050854 6.775 .00050068 8 .040 6.554 .00100923 .00050854 Experiment 10. Absorption of Water and Evolution of Carbon Dioxide by Corn Roots. Experiment No. 11. This experiment was carried out under similar conditions to those of Experiment 10 and simultaneously with it. The general correlation between the curves of respiration and absorption is evident, the discrepancies appearing in the initial two hours of the experiment. Absorption, singularly enough, rose from an initial low value during the period of exposure to moist air, and this rise was much greater than that shown in Experiment 10. During the course of the sth hour exposure to dry air the absorption rate decreased to the original minimum value. The rate of carbon dioxide evolution showed a general and variable decrease throughout the course of the experiment. The absolute values of absorption are similar to those of Experiment 10, but the respiration rates are conspicuously less. It seems probable that the plants used in Experiments 10 and 11 were gradually becoming abnormally inactive. For this reason the absolute values obtained in these experiments must be used with caution. The correlation between the respirational and absorption activities holds even in this extreme case. This experiment was carried out from 7*oo A.M. to 3:00 P.M. February 1, 1931. The roots were placed in rain water. The leaves were surrounded with moist air for three hours and then with dry air. The plant was 1 1/2 weeks old and 12 inches high, the length of the roots being 6 inches. During the time of the experiment in hours as abscissae, the curves show; point, rate of respiration; and point-triangle, rate of absorption of water. The ordinates on the left side of the graph represent the rate of respiration in cubic centimeters of carbon dioxide per hour. The ordinates on the right side of the graph represent the rate of absorption of water in cubic centimeters per hour. General Course Of Respiration and Absorption in Rain Water. In order to emphasize the general relation between water absorption and carbon dioxide evolution which these experiments show, the averages of all observations at the various periods have been calculated and plotted in Fig. 4. In obtaining these averages the values for the first hour have been omitted because they seemed to some degree to reflect preceding conditions. The period of exposure to moist air was taken as four hours, and the values obtained in experiments in which the moist period was greater than this have been omitted in the average of the values obtained in dry conditions. The general course of water absorption and respiration is indicated in Fig. 4 disregarding the minor variations so as to compare the general course of the two processes. The respiration curve has not been drawn through the high point at the fifth hour because the low values in Experiments 8 and 9 were obtained under moist conditions. Since the general respiration level was low in these experiments and since these values appear in the averages after the fifth hour, the apparent fall in respiration from the fifth to later hours was not real. The general correlation of absorption and carbon dioxide evolu- tion by the root system of corn in rain water indicates a close relationship between these activities. Absorption of Water and Evolution of Carbon Dioxide by Corn Roots. Figure 4. GENERAL COURSE OF RESPIRATION. AND r ABSORPTION IN 'RAIN WATER Time hours Absorption co ’s per hr Observed PH Total COs content of solution, cc COg evolved cc ’s per hour. 6.860 .000389620 1 .025 6.605 .000866927 .000477307 6.826 .000429330 2 • 055 6.605 .000866927 .000437597 6.775 .000500685 5 .075 6.605 .000866927 .000366242 6.775 .000500685 4 .060 6.605 .000866927 .000366242 6.775 .000500685 5 .040 6.656 .000725630 .000224945 6.775 .000500685 6 • 020 6.656 .000725630 .000224945 6,775 .000500685 7 .025 6.690 .000651556 .000150871 6.775 .000500685 8 .030 6.656 .000725630 .000224945 Experiment 11. Absorption of Water and Evolution of Carbon Dioxide by Corn Roots. Experiment No. 14. In order to avoid any buffer or physiological effect of the salts contained in rain water, Experiment 14 was carried out in distilled water, the plant having been transferred to this medium twelve hours before the beginning of the experiment. The water was thoroughly aerated by bubbling air slowly through it for twelve hours. The results are given in the table and the values for water absorption and evolution of carbon dioxide of the root system are shown in the graph. The close correlation between carbon dioxide evolution and absorption is evident during the initial seven hours of the experiment. During the remainder of the experiment this relation was subject to considerable variation. During the first three hours of the period of observation the rate of absorption remained low, rising after the change to dry air to a maximum in two hours. After this time the rate of absorption gradually fell throughout the course of the experiment, the decrease being especially rapid during the last hour. Respiration rates showed gradually increasing values during the first five hours of the experiment. They fell slightly and later increased to a maximum at the ninth hour. In absolute values, the results obtained for absorption of water in Experiment 14 are similar to those given in Experiments 1,2, 3,4, 7, 10, and 11. In contrast to this the rate of carbon dioxide evolution was markedly higher than in any experiment in which rain water was employed, the maximum values being 0.02 in Experiment 4 compared to 0.12 in the present experiment. This result seems to be due to the calcium carbonate present in Austin rain water and the consequent formation of the bicarbonate. Variations in the rate of respiration during the latter part of the experiment may have been due to abnormal conditions developing in the plant while under observation. It is evident that even under unsatisfactory conditions the general course of respiration parallels that of absorption. This experiment was carried out from 7:00 A.M. to 8;00 P.M. February 7, 1931. The roots were placed in distilled water. The leaves were surrounded with moist air for three hours and then with dry. The amount of water surrounding the roots was 90 cc. The plants were one week old and 13 Inches high, the length of the roots being 6 inches. During the time of the experiment in hours as abscissae, the curves show; point, rate of respiration; and point-triangle, rate of absorption of water. The ordinates on the left side of the graph represent the rate of respiration in cubic centimeters of carbon dioxide per hour. The ordinates on the right side of the graph represent the rate of absorption of water in cubic centimeters per hour. Absorption of Water and Evolution of Carbon Dioxide by Corn Roots. Time hours Absorption co ’s per hr Observed pH Total COg content of solution cc. GOg evolved cc’s per hour. 6.265 .002811863 1 .025 5.925 .010531719 .007719856 6.010 .007467946 2 .025 5.755 .021337565 .013869619 5.840 .014916049 3 .020 5.585 .047770668 .032854619 5.840 .021337565 4 .042 5.500 .063962304 .049046255 5.840 .021337565 5 .080 5.449 .079718562 .064807513 5.670 .032048676 6 .060 5.415 .085989442 .053940776 5.585 .047770668 7 .060 5.415 .085989442 .038218774 5.381 .047770668 8 .050 5.204 .227767320 .119769329 5.381 .107997991 9 .040 5.170 .276870330 .168882339 5.381 .107997991 10 .050 5.255 .188865470 .080867479 5.381 .107997991 11 .045 5.255 .188865470 .080867479 5.330 .135432867 12 .040 5.255 .188865470 .053432603 5.330 13 .010 5.221 .215769782 .080336915 Experiment 14. Absorption of Water and Evolution of Carbon Dioxide by Corn Roots. Experiment No. 15. This experiment was carried out in a manner similar to that described for Experiment 14 except that the initial exposure to dry air was four hours in length. The plant used was one week old. The curves of absorption and respiration show a close correlation throughout the course of the experiment. The values remained at a low level during the initial four hours during which the plant was subjected to moist air. Upon exposure to dry air absorption rose quickly during the first hour and increased steadily to a maximum during the following four hours, falling slightly toward the end of the experiment • During the initial four-hour period of exposure to dry air respiration rose slightly and increased during the remainder of the experimental period, reaching a maximum during the final hour. The range of absolute values of absorption rates is not conspicuously different from that of Experiment 14. The respiration rates are considerably higher and show values greater than those for any other experiment, reaching a final maximum of nearly 2.4 cc per hour. This plant showed great activity in both absorption and respiration and gave no indication of abnormal behavior during the course of the experimental period. It is evident that in this plant the respiratlonal and absorptive activities of the root were closely paralleled. This experiment was carried out from 7;00 A.M. to 6;00 P.M. February 8, 1931. The roots were placed in distilled water. The leaves were surrounded with moist air for four hours and then with dry air. The amount of water surrounding the roots was 90 cc. The plants were one week old and 15 inches high, the length of the roots being 6 inches. During the time of the experiment in hours as abscissae, the curves show; point, rate of respiration; and point-triangle, rate of absorption of water. The ordinates on the left side of the graph represent the rate of respiration in cubic centimeters of carbon dioxide per hour. The ordinates on the right side of the graph represent the rate of absorption of water in cubic centimeters per hour. Absorption of Water and Evolution of Carbon Dioxide by Corn Roots* Time hours Absorption co per hr. Observed PH Total C0 2 content of solution cc. C0 2 evolvedcc ’s per hour. 5.789 .01849148 - 1 • 020 5.204 .22776732 .19927584 * 5.500 .06396230 2 .020 5.119 .34406975 .28010744 * 5.415 .08598944 3 .015 5o085 .40694989 .32096045 5.289 .16250089 4 .015 5.000 .59602475 .43352385 5.255 .18886547 5 .075 4.881 1.02192948 .83306501 5;255 ;18886547 6 .075 4.917 .85418792 .66532245 5.170 .27687033 7 .085 4.796 1.50368208 1.23681175 5.119 .34406975 8 .085 4.745 1.89974070 1.55567095 5.119 .34406975 9 .100 4.745 1.89974070 1.55567095 5.102 .37022671 10 .075 4.745 1.89974070 1.52951399 5.085 .40694989 11 .080 4.660 2.80144845 2.39449855 Experiment 15 Absorption of Water and Evolution of Carbon Dioxide by Corn Roots. Experiment No. 16. Experiment 16 was carried out simultaneously with and under similar conditions to those of Experiment 15. The results are very similar to those just discussed, except that there was slightly greater respirational activity during the middle portion of the experimental period. The correlation between the rates of absorption and respiration is good, both rates remaining at low levels during the initial four-hour period and rising to maximum values at the ninth hour. The range of absolute values in this experiment is similar to that of Experiment 15. The activity of the plant used in this experiment was as great as that employed in 15. As in Experiment 15 this plant passed through the experimental period in a highly active condition. The results of this experiment show a marked similarity to those of Experiment 15 and again show strikingly the close parallelism between the absorptive and respirational activities of the root system. This experiment was carried out from 7:00 A.M. to 6:00 P.M. February 8, 1931. The roots were placed in distilled water. The leaves were surrounded with moist air for four hours and then with dry air. The plant was one week old and 15 inches high, the length of the roots being 6 inches. During the time of the experiment in hours as abscissae, the curves show; point, rate of respiration; and point-triangle, rate of absorption of water. The ordinates on the left side of the graph represent the rate of respiration in cubic centimeters of carbon dioxide per hour. The ordinates on the roght side of the graph represent the rate of absorption of water in cubic centimeters per hour. Absorption of Water and Evolution of Carbon Dioxide by Corn Roots. Time hours Absorption co ’ s per hr Observed pH Total COg content or solution, cc C02 evolved, cc *s per hour. 5.500 .0639634 1 .030 5.000 .5960247 .5320624 5.500 .0639634 2 .015 5.136 .3295569 .2655946 5.515 .0859894 3 .020 5.119 .3440697 .2580803 5.289 .1625009 4 .005 4.915 .8598949 .6916870 5.255 .1888654 5 .050 4.830 1.2887206 1.0998551 5.255 .1888654 6 .045 4.779 1.6279256 1.4381611 5.170 .2768703 7 .045 4.745 1.8997407 1.6228704 5.119 .3440697 8 .060 4.711 2.2172040 1.8731343 5.119 .3440697 9 1090 4.610 2.8014485 2.4573788 5.102 .3702267 10 .065 4.660 2.8014485 2.4312218 5.102 .3702267 11 .070 4.660 2.8014485 2.4312218 Experiment 16. Absorption of Water and Evolution of Carbon Dioxide by Corn Roots. Experiment No. 17. Experiment 17 was carried out with the root system of the plant in distilled water and with tops exposed to dry air during the entire course of the experiment. Absorption was measured in the usual way. Resplrational activity was followed both by the measurement of the evolution of carbon dioxide and of oxygen consumption. The values obtained by these tnree measurements are tabulated together with tne computed respiratory quotient, and the curves showing absorption, carbon dioxide evolution and oxygen consumption are graphed. The curves show a good general correlation, the discrepancy being the high values for the absorption rates of the sixth and eighth hours. From the initial high value the curves fell to a minimum during the second hour and rose to a moderately high level for the remainder of the experiment except for the three high absorp tion rates just mentioned. It is evident from these results that the rate of respiration may be measured either by the evolution of carbon dioxide or by the consumption of oxygen with similar results. The absolute values of both respiration and absorption show a range similar to that of the preceding three experiments. The respiratory quotient remained approximately constant, the values averaging 0.68, and showing an extreme variation from 0.91 to 0.61. This experiment was carried out from 7:00 A.M. to 4;00 P.M. February 28, 1931. The roots were placed in distilled water. The leaves were surrounded with moist air for two hours and then with dry air. The plant was one week old and 12 Inches high, the length of the roots being 5 inches. During the time of the experiment in hours as abscissae, the curves show; point, rate of carbon dioxide evolution; point triangle, rate of absorption of water; and point-square, rate of absorption of dissolved oxygen. The ordinates on the left side of the graph represent the rate of respiration in cubic centimeters of either carbon dioxide or of oxygen. The ordinates on the right side of the graph represent the rate of absorption of water in cubic centimeters per hour. General Course of Respiration and Absorption in Distilled Water. The general course of root respiration and water absorption is shown in Fig. 5, in which the initial four-hour period was carried out with the plant in moist air and the remainder of the period in dry. For reasons previously explained in connection with the averages of the plants observed in rain water, the readings made at the first hour have been omitted. All readings made after the tenth hour have been omitted because this was the duration of Experiment 17. It will be seen that during the moist period absorption remained at a relatively constant low value. A comparison with the results of the plants observed in rain water (Fig. 4) shows that in distilled water, values are more constant, but of a similar magnitude. When shifted to dry conditions the plants in distilled water showed a rapid rise to a maximum value which was maintained with small variations. This behavior is in contrast to that of the plants in rain water where minimum values were not attained until the tenth hour. In distilled water the curve of carbon dioxide evolution increased rather uniformly throughout the course of the plotted period, and showed only aminor increase coincident with the shift to dry conditions. Although the general course of respiration of the plants observed in distilled water followed that of absorption, as occurred in rain water, the correlation is not so perfect. In view of the fact that the plants had been kept in distilled water for twelve hours preceding the experiment, it does not seem probable that the gradual increase in the respiratory rate was due to a permeability effect. It appears that this effect is more conspicuous in the average of the comparatively few experiments than is really the case in the experiments themselves. A comparison of the graphs of Experiments 14, 15, 16, and 17 shows that the increase in the rate of carbon dioxide evolution following the advent of dry conditions was not as rapid as might be expected from the course of absorption. This may have resulted from a transfer of dissolved carbon dioxide through the plant and a consequent delay in the evolution of this gas until an equilibrium at the partial pressure in the roots had been attained throughout the tissues. Since the plants were kept in darkness this equilibrium was not disturbed by photosynthetic activity. The time necessary for establishing this equilibrium would have varied with the rate of absorption and the consequent transpiration stream. The curve of the respiration rates of the plants in distilled water, in which the transpiration quickly rose to a maximum exceeding that attained in rain water, shows this delay. Plants in distilled water reached a maximum rate of absorption more quickly and at a greater value than those in rain water. The rate of carbon dioxide evolution increases more gradually but to an apparent higher value in distilled water than in rain water, probably because of the action of the mineral solutes of the latter. Saturation of the tissues with carbonic acid distributed by the transpiration stream may have produced the apparent delay in respiratory response. Absorption of Water, Evolution of Carbon Dioxide and Absorption of Dissolved Oxygen by Corn Roots. Figure 5. Tim© hours HgO Absorption oc ’s per hr. COg Evolution go’s per hr. 0 2 Absorption cc ! s per hr. R.Q. 1 .045 .19089 .212 .91 2 • 020 .07137 .085 .84 3 .030 .07769 .127 .61 4 .035 .10339 .169 .61 5 .035 •10339 .169 .61 6 .050 •10339 .169 .61 7 .060 .10339 .169 .61 8 .060 .10961 .169 .64 9 • 030 .10961 .169 .64 Experiment 17. Absorption of Water, Evolution of Carbon Dioxide and Absorption of Oxygen by Corn Roots. Experiment No. 18. It is obvious that the measurement of the respiration rate by means of the micro-Winkler method offers some advantages over the electrometric method of estimating the evolution of carbon dioxide in that any buffer action of the solution does not interfere with readings. The micro-Winkler method can thus be used with equal facility in distilled water, rain water or nutrient culture solution. This method was therefore employed in the remainder of the observations. In Experiment 18 the rate of respiration of the roots of a plant one week old was followed for six hours with the root system in aerated distilled water and the tops subjected to dry air. The results are tabulated and those for oxygen and water absorption graphed. It will be seen that the two processes paralleled each other closely throughout the course of the experiment, a single discrepency occurring between the third and fourth hours. The rates of both respiration and absorption increased to the third hour when there was a slight decrease in respiration but no change in absorption. The rates of both processes rose to a maximum at the fifth hour and fell to a lower value at the sixth. These variations may have been due either to changes in the rate of flow of the air over the tops or to periodic fluctuations in the plant itself. The range of absolute values for the rates of both respiration and absorption is similar to that in Experiment 17. In the course of the closely correlated rates of the absorp- tion of oxygen and of water it will be seen that ,the values of the latter are slightly higher than those of Experiments 14, 15 and 16. The respiration rates are, however, within the range of those observed in these experiments. This experiment was carried out from 10:00 to 4:00 P.M. February 28, 1931. The roots were placed in distilled water. The leaves were surrounded with dry air during the entire experiment. The plant was one week old and 10 inches high, the length of the roots being 5 inches. During the time of the experiment in hours as abscissae, the curves show; point, rate of respiration; and point-triangle, rate of absorption of water. The ordinates on the left side of the graph represent the rate of respiration in cubic centimeters of oxygen per hour. The ordinates on the right side of the graph represent the rate of absorption of water in cubic centimeters per nour. General Course of Respiration and Absorption in Distilled Water. In order to secure a more definite understanding of the general course of absorption and respiration as measured in distilled water by the consumption of oxygen, the curves shown in Fig. 6 have been drawn. The values, beginning with the second hour, are the averages of two observations. The plants were subjected to dry air throughout the course of the experiments. The correlation of the curves is very close throughout the period of observation. Both curves rise to maxima at the fifth hour and fall to a lower value at the sixth. The absolute values of absorption are in a range similar to that shown in the general curve in Fig. 5 for plants in distilled water, but above that shown in Fig. 4 for plants in rain water. Assuming a respiratory quotient of 0.7, the respiratory activity shown in Fig. 6 is below that shown in Fig. 5 for the plants in distilled water, but greatly in excess of the apparent rate shown in Fig. 4 for plants in rain water. Absorption of Water and of Dissolved Oxygen by Corn Roots. Figure 6. Time hours Water absorption cc ’s per hr. Og absorption cc ’s per hr. 1 .040 .085 2 .070 .127 3 .080 .169 4 .090 .127 5 .112 .169 6 .070 .085 Experiment 18. Absorption of Water and of Dissolved Oxygen by Corn Roots. Experiment No. 19. In Experiment 19 the plant was observed in fresh Knop’s solution of the same concentration as that in which they had been grown. The rates of absorption and those of respiration as measured by oxygen consumption were observed through a period of eight hours. The results have been tabulated and graphed. The conditions of this experiment would be expected to be more nearly normal for the plant than those in which either distilled water or rain water was used. The correlation between the two processes is very close. The plants were kept in moist air only for the initial hour. The first value for the absorption of both oxygen and water is low. With a change to dry conditions both rates rose rapidly until a maximum for respiration was reached at the end of three hours. After this time the rates fluctuated simultaneously at a moderately high level to the end of the experiment. The rates of respiration paralleled those of absorption closely throughout the experiment. The absolute values for absorption are similar to those of Experiment 18. Respirational values are higher, however. This experiment was carried out from 8:00 A.M. to 4:00 P.M. April 21, 1931. The roots were placed in nutrient solution. The leaves were surrounded with moist air for one hour and then with dry air. The amount of culture solution surrounding the roots was 90 cc’s. The plants were one week old. During the time of the experiment in hours as abscissae, the curves show; point, rate of respiration; and point-triangle, rate of absorption of water. The ordinates on the left side of the graph represent the rate of respiration in cubic centimeters of oxygen per hour. The ordinates on the right side of the graph represent the rate of absorption of water in cubic centimeters per hour. Absorption of Water and of Dissolved Oxygen by Corn Roots. Time hours Water absorption cc ’s per hr. Os absorption cc ’s per hr. 1 .020 .215 2 .050 .355 3 .090 .372 4 .110 .338 5 .060 .279 6 .075 .322 7 .060 .245 8 .120 .322 Experiment 19. Absorption of Water and of Dissolved Oxygen by Corn Roots. Experiment 20. This experiment was carried out simultaneously with and under the same conditions as Experiment 19. The results obtained have been tabulated and graphed. There is a very good correlation between respiration and absorption, the two processes paralleling each other throughout the experiment. From the initial low values obtained under conditions of moist air the maximum rates for both respiration and absorption were reached at the fourth hour, after which the two processes varied simultaneously and to the same degree. The absolute values for absorp tion were less than those of Experiments 18 and 19, and respirational values were greater than those of Experiment 18 but similar to those of 19. The general course of the two processes in the two plants on Experiments 19 and 20 is the same. This experiment was carried out from 8:00 A.M. to 4:00 P.M. April 21, 1931. The roots were placed in nutrient solution. The leaves were surrounded with moist air for one hour and then with dry air. The amount of culture solution surrounding the roots was 90 cc ! s. The plants were one week old. During the time of the expeh. ment in hours as abscissae, the curves show; point, rate of respiration; and point-triangle, rate of absorption of water. The ordinates on the left side of the graph represent the rate of respiration in cubic centimeters of oxygen per hour. The ordinates on the right side of the graph represent the rate of absorption of water in cubic centimeters per hour. Absorption of Water and of Dissolved Oxygen by Corn Roots. Time hours Water absorption co ’s per hr. Og absorption cc * s per hr. 1 .020 .229 2 .030 .269 3 .030 .322 4 .050 .364 5 .025 .169 6 .035 .279 7 .025 .127 8 .040 .152 Experiment 20. Absorption of Water and of Dissolved Oxygen by Corn Roots. Experiment No. 21. Experiment 21 was carried out under conditions similar to the two preseding experiments, except that the initial moist period was three hours. Since this plant had been kept for the 12 hours preceding the experimental period in nutrient solution which was replaced by freshly aerated medium, the initial rates of oxygen absorption were high. As equilibrium between the tissues and the medium was attained, the rate of oxygen absorption fell to a value proportionate to the water absorption. After this adjustment the curves of absorption of water and of oxygen parallel each other closely, no discrepancies occurring during the remainder of the experiment. The rates of both processes increased with the advent of dry conditions at the end of the third hour, and then decreased toward the end of the experimental period. Absorption and respiration values are within the range of those of Experiment 18 and respiration is similar to that observed in Experiments 19 and 20. This experiment was carried out from 8:00 A.M. to 4:00 P.M. November 27. 1931. The roots were placed in nutrient solution. The leaves were surrounded with moist air for three hours and then with dry air. The amount of water surrounding the roots was 90 cc’s. The plants were one week old. During the time of the experiment in hours as abscissae, the curves show; point, rate of respiration; and point-triangle, rate of absorption of water. The ordinates on the left side of the graph represent the rate of respiration in cubic centimeters of oxygen per hour. The ordinates on the right side of the graph represent the rate of absorption of water in cubic centimeters per hour. ral Course of Respiration and Absorption in Cultuxe Solution. The general course of respiration and absorption in culture solution is shown in Fig. 7. For reasons already given the readings for the initial hour have not been used, all other values are averages of those obtained in three experiments. A very close correlation between absorptive and respirational activities exists throughout the eight hours duration of the observation period. Since the readings for the first hour have been omitted all averages represent behavior under conditions of dry air. A comparison of these curves with those of Fig. 6 shows that the range of absorption values is similar. In contrast to this, respiration values are considerably higher. Since the values used in Fig. 6 have been obtained from the observations on plants kept in distilled water while those of Fig. 7 were derived from similar readings made while the plants were in culture solution, the difference between the respiration levels may be significant. Obviously any absorptive activity of the root systems in Knop's solution would take place against osmotic resistance. The additional work involved is shown by the higher respiratory curve of Fig. 7. Absorption of Water and of Dissolved Oxygen by Corn Roots. Figure 7. Time hours Water absorption Og absorption cc’s per hr. cc’s per hr. 1 .05 .4485 2 .05 .1692 3 .05 .1777 4 .07 .2369 5 .07 .2369 6 .07 .2369 7 .04 .1015 8 .05 .1269 Experiment 21. Absorption of Water and of Dissolved Oxygen by Corn Roots. DISCUSSION AND CONCLUSIONS The conception of an organism as a mechanism operated by the expenditure of energy is basic in much of the work of the animal physiologist. Animals so frequently display the channels of energy dissipation in movement and maintenance of body temperature that it seems but natural to consider many activities possible only with a supply of available energy and to regard as evidences of the activity not only the reaction itself but also the gaseous exchange of respiration. That the vast majority of the processes occurring in the animal body are endothermic is hardly open to doubt. Muscular activity is associated with a proportionate degree of respiratory activity (Bayliss 1924) in which carbohydrates are directly concerned (Evans 1926). So firmly has this conception become established that respiratory activity is taken as a measure of work done even when the exact nature of this work is not evident, as in the nucleated red blood corpuscles and in the cells of the central nervous system (Bayliss 1924). For the animal the source of energy, and hence the driving force of physiological activity is to be found in the exothermic reactions involved in respiration. An evaluation of the work done by an animal can be made by a measurement of respirational activity. This is essentially oxidation. When no visible work is being done there is still measurable respiration which is then the measure of the minimum work for that animal necessary for the maintenance of the life processes. It would seem that the plant physiologist, working in a field separated from that of his coworker with animals only by degree, would have quickly accepted this clarifying and profitable conception as basic. It is a curious fact, however, that the plant physiologist too frequently is unwilling to assign an endothermic role to any activity if by any assumption it can be supposed to proceed otherwise. While the energy relations of photosynthesis have been studied in detail by Brown and Escombe (1900), no such investigations have been reported for other important endothermic plant activities. Thus we know from the results of physics and chemistry how to evaluate respiration in terms of energy, but do not possess such knowledge concerning the use of this energy in the plant. For instance, in the fundamentally important water relations many workers have hesitated to assign any physiological energy relation. Following the work of Dutrochet (1887), explaining water absorption as a function of osmotic pressure influenced by the plant only through changes in the concentration of the solutes or the permeability of the membranes, extensive studies have been reported on osmotic concentrations. The osmotic mechanism is perhaps the most widely accepted explanation of water absorption and transport at the present time. This explanation is accepted in spite of the fact that many of the gradients of concentration along the paths of absorp- tion and transport do not agree in direction with that of movement of water. Thus Ursprung and Blum (1916) have shown that while there is a gradient of Increasing concentration from the root hairs to the endodermis the gradient is in the opposite direction from this tissue to the xylem vessels. Following the work of Sachs (1887) imbibitional forces have been accepted by many workers as an explanation of water absorption. Kunkel (1912) believes that these forces are the main ones in the intake of water by the roots, and that osmotic forces play no part whatever. Shull (1924) assigns an important role to imbibitional forces but does not exclude osmotic forces. According to this conception the energy for absorption would be the absorbed radient energy necessary for vaporization in the aerial parts of the plant. Both the osmotic and imbibitional explanations of water absorption and transport fail to satisfactorily explain exudation or root pressure and also the fact that an oxygen supply is necessary for root activity. Similarly guttation is explained with difficulty on this basis. In order to explain water transport under these conditions various hypotheses have been suggested. Priestley (1924) believes the endodermis acts as the functional absorbing surface of the root; he assigns to it the role of a semi-permeable membrane, separating the intercellular cortical fluids from those of the xylem vessels. Pfeffer (1877) formulated a hypothesis based on differences in the osmotic pressure of the plasma membrane in different parts of the cell to explain movement of water from a high concentra tion to a low one. Although he later abandoned this as being unlikely, Lepeschkin (1906) used it to explain exudation of water by sporangiophores and by hydathodes. More recently workers coming from the field of animal to general physiology have considered that osmotic work must be done (Burns 1929, and Scarth and Lloyd 1930). The actual mechanism Involved is not clear. A secretory action may take place in the endodermis or in other tissues, but since the mechanism of glandular activity has not been satisfactorily explained, such a hypothesis is not very clarifying. Similarly electroendosmosis is a possible explanation but until more facts substantiating this have been found such an assumption is of little value. It is apparent upon reflection that irrespective of the mechanism involved, osmotic work must be done. Any system of cells along the line of water absorption and transport must show a gradient of increasing osmotic pressure from root hair to leaves. This will be seen to be true whether the osmotic or imbibitional mechanism is assumed, since in any active cell there will be an equilibrium between the surface forces in the colloidal boundaries and the osmotic activities of the sap solutes. Since the actual concentration gradient does not conform to this requirement and since positive exudation pressures are not thus explicable these theories must be modified. If work is accomplished the necessary energy must be furnished directly or indirectly by respiratory processes and can be detected and estimated by them. The present study was undertaken with this in view. The results obtained from a simultaneous measurement of water absorption and root respiration as measured by changes of pH in rain water show a general close correlation between the two processes in all the experiments. Even in the two experi ments where the plants were kept in the light this relation continued. Wen transpiration was increased by a change from high to low humidity around the leaves, the rate of absorption increased accompanied by a similar increase in the rate of carbon dioxide evolution. In some experiments where the rate of absorption was rapidly and considerably increased there was an apparent lag, or even a fall in the rate of respiration (Experiments 3,9, and 11). This was probably due to some of the carbon dioxide being carried up in the transpiration stream. Since these plants were kept in darkness during the entire course of the experiment, carbon dioxide was not used in photosynthesis and the tissues ultimately became saturated with it. From this point the evolution of carbon dioxide from the roots increased and paralleled absorption for the remainder of the experiments. The two processes varied similarly due either to variations in external conditions or to periodicity in the behavior of the plant. This may be the explanation of the decreasing values toward the end of Experiments 1,6, 7, 8, and 10. It appears that in rain water the corn seedlings show a correlation between the rates of carbon dioxide evolution from the root system and the water absorption. If the minor variations are disregarded the general correlation of the two processes may be seen in Fig. 4. When the carbon dioxide evolution was followed in aerated distilled water a correlation similar to that observed in rain water appears. In general this correlation was somewhat more perfect than that observed in rain water although the resplrational lag was somewhat greater when absorption was increased by the change to dry conditions. The general courses of carbon dioxide evolution and water absorption (Fig. 5) shows that the respiratory response of these plants based on the averages of the various observations shows very little response to the sudden increase in absorption. This appears to be the result of the upward transport of carbon dioxide dissolved in the transpiration stream. It constitutes a serious difficulty in correlation studies such as this. When the absorption of oxygen is followed in aerated distilled water most of this difficulty disappears and the correlation with absorption Is much better (Fig. 6). No lag appears in the curves. Apparently the transport of oxygen in the absorption stream is negligible in amount. This is to be expected from the fact that more soluble carbon dioxide is formed within the tissues and thus along the course of the absorption stream, while the less soluble oxygen enters the tissues from the surface and is used by all living cells with which the solution comes in contact. The curves shown in Fig. 6 show that the rate of oxygen absorption initially increased more rapidly than absorption, but came to a rate more comparable with that of absorption after the third hour. This possibly shows a period during which an oxygen deficit, which had been developed in the active tissues under great absorptive activity, was becoming reduced. The values for the absorption of oxygen, although subject to such minor 'variations are more closely correlated with absorption than are the rates of carbon dioxide evolution, and offer a better measure of the metabolic activities of the root system. Plants which were observed while the root systems remained in fresh Knop’s solution similar to that in which the seedlings were grown, show a close correlation between the absorption of oxygen and of solution. This correlation is similar to that observed when the plants were 'transferred to aerated distilled water and indicates that no abnormal conditions developed during the course of the experimental period in the salt free medium. The levels of the respirational values obtained in Knop’s solution were higher than those obtained when the root systems were in distilled water, but the correlations found were similar. In spite of the precaution of collecting rain water only after considerable rain had washed the air and roof, there were some buffering salts present in it. The acidity measurements used for estimating the carbon dioxide do not represent the true values. Results obtained in distilled water for carbon dioxide evolution are more trustworthy and may be compared with the values obtained for oxygen absorption both in distilled water and in Knop’s solution. If from the values in Experiments 14 and 17 the average amount of carbon dioxide evolved per cubic centimeter is computed, it is found to be 2.1. In this average, Experiments 15 and 16 have not been used because the plants showed a much higher though proportionate rate of respiration, and are thought to be abnormal in this respect. If we accept an energy value of 5.047 small calories per cubic centimeter of carbon dioxide, we have 10.60 calories per cubic centimeter of absorption of of distilled water. Averages of oxygen absorption per cubic centimeter of water absorbed by the roots in distilled water gives a value of 2.3 cubic centimeters, equivalent to 11.61 calories. As computed by the absorption of oxygen, respiration shows 9.5 per cent increase over the value as calculated from the carbon dioxide evolved. The plants used in Experiments 19, 20, and 21 were not changed to water from the Knop’s solution in which they had been growing, the absorption of oxygen being followed in freshly aerated medium. The average consumption of oxygen per cubic centimeter of absorption for these plants is 4.6. This corresponds to an energy value of 23.22 calories, an increase of 12.21 or 110 per cent over that observed in distilled water. There is no obvious reason for this greatly increased oxygen consumption by the root system except the osmotic resistance offered by Knop’s solution. Since this medium has an osmotic concentration of 1.75 atmospheres, a resistance of this amount necessitates the expenditure of 12.21 calories, and since this is 110 per cent of the energy requirement for absorption of distilled water, the value for this process may be considered to 1.75 be that of the requirement for absorption against xloo~ 1.59 atmospheres. Since the rate af absorption did not remain constant but varied with slight changes in the conditions to which the tops were subjected, the work involved may be compared at different absorptive rates. For capillary tubes and for moderate current speeds the flow should bear a linear relation to the pressure or energy involved. At high rates of absorption the efficiency should be low and the plant show a greater respiratory value per cubic centimeter of water absorbed. If the amount of carbon dioxide evolved in distilled water is computed per cubic centimeter of absorption, we have 2.0, and 2.5 at the periods of maximum and minimum absorption com- pared to 2.1 for the average. The highest value appears with the lowest rate of absorption. This may be interpreted as a result of the removal of carbon dioxide from the root in the transpiration stream, but this evidence could not be interpreted as confirmatory because similar transport of oxygen is not shown. The values obtained for oxygen absorption agree very well with those for carbon dioxide evolution, being for maximum, minimum and average rates of absorption, 2.0, 2.8, and 2.3 respectively. As measured both by the evolution of carbon dioxide and the absorption of oxygen the root system of corn shows the highest efficiency at the highest rate of water absorption. A similar relation holds for the consumption of oxygen when the plants are observed in Knop’s solution, the values being 4.4, 5.1, and 4.6 at maximum, minimum and average absorption rates. These facts may be interpreted in one of two ways; the corn seedlings are more efficient absorbing machines at the higher absorptive rates than at the lower. This does not seem improbable as under field conditions absorption demands are often more severe than those of the present study. A second interpretation is also possible. The respiratory activity of roots as expressed either by the evolution of carbon dioxide or by the absorption of oxygen is the sum of the basal metabolic activities of the tissue and of other activities such as the osmotic work involved in absorption. This basal activity may be assumed to be constant in a given root system under the stable conditions and during the short period of these experiments. The fraction of the observed respiratory values due to basal metabolism will thus vary with the time, but when absorptive efficiency is compared, the time Interval is least when the rate of absorption is highest. It thus appears that the greater the rate of absorption the smaller is the observed respiratory value due to the basal respiration, and the lower the rate of absorption the more this value is made up from the basal source. According to this view the reason why the respiratory rates are lower when rapid absorption is in progress is that the time required for one cubic centimeter of water absorption is small and hence includes a small fraction of basal respiration. When time is made constant and the respiratory activity expressed as rate, we have, as the curves show, respiratory activity proportional to absorptive. In this, basal respiration is a constant, so that the positive correlation shown may indicate the real relation, which is that of greater efficiency at lower absorptive rates. Although the consideration of absorptive efficiency does not furnish evidence pointing to carbon dioxide transport, the respiratory quotients obtained in Experiment 17 do. Thus the values for high and low rates of absorption are 0.61 and 0.84 respectively, the average being 0.69. This seems to indicate the transportation of carbon dioxide in the absorptive current. SUMMARY 1. A method was devised for growing corn seedlings under sterile conditions to secure active, uniform, and normal growth in liquid culture in the laboratory. 2. A method was developed for obtaining the simultaneous measurements of root respiration and water absorption. 3. The carbon dioxide evolution of roots is measured by the change in the pH of the medium. This is practicable only in the absence of buffering salts, and hence with the root system in distilled water. 4. The oxygen absorption of the roots was measured by the micro-Winkler method. 5. In aerated rain water the rates of absorption and carbon dioxide evolution show a positive correlation. 6. The absolutes values for carbon dioxide evolution obtained in rain water are low because of the buffer action of traces of salts present. 7• In aerated distilled water, a positive correlation between the rates of carbon dioxide evolution and water absorption is shown. 8. The absolute values obtained in distilled water are higher than those in rain water. 9. The rates in distilled water more nearly express the true respiratory activity of the roots than do those in rain water. 10. Absorption of oxygac in distilled water correlates closely with water absorption. 11. The respiratory quotient Is less than 1, varying between 0.61 and 0.91. 12. The higher values of the respiratory quotient correspond with low rates of water absorption, indicating the transpor~ tation of carbon dioxide from the root. 13. The rates of absorption of water and of oxygen by the roots in Knop’s solution show a positive correlation. 14. The rate of oxygen absorption in Knop’s solution is greater than that in distilled water. 15. The absorption of water by corn roots is accompanied by a liberation of energy which has been computed from the res piratory exchange. 16. In the absorption of one cubic centimeter of distilled water 11.61 calories of energy were liberated. 17. 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