Studies of the effective factors and the importance of tillering in cultivated and native grasses



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The grass seedling appears as a single spear, which may or may not, according to the species, start branching at or near the surface of the ground relatively early in its ontogeny. This branching is called tillering, stooling, or mooting. "Bestockung," says Nowacki in his "Anleitung zum Getreidebau," as quoted by Rosler (1928), "ist eine Verzweigung des Stammes in der Nahe der Wurzel." This definition does not exclude stolons and rhizomes, but the term "tillering" is usually, at least, restricted to those branches which arise intravaginally, and it will be so used during the course of this discussion. In most grasses this occurs in a region made up of several nodes, the internodes between which have been more or less completely reduced. The maximum primary tillering capacity (regarded as the maximum number of primary tillers possible from the primary axis of the individuals of a species) must be dependent upon the number of bud primordia, a structural characteristic which is probably to be regarded as specific. The number of primary tillers developing in a given set of conditions varies within the limits of this maximum under the impress of different climatic and edaphic complexes. Such factor complexes are important to tillering as they affect the nutrition and development of the plant. The ecological importance of the number of tillers produced and of the time of their development could be expected to be considerable, because of their possible influence on competition and ecisis. Comparatively little work has been done with cereals, and less with native grasses on either the isolation of effective factors or the evaluation of their importance to the species. An attempt to isolate and compare the effects of some of the environmental factors seemed profitable. In evaluating effects of these factors it is desirable to have a standard for comparison. One such standard for tillering of a species is the number of tillers obtained in a given time under the best of environmental conditions. This optimum set of conditions will, of course, vary with the species and may be determined only after an analysis of the single factors. The present work is a beginning in that direction