74 THE WHEAT PLANT 



varieties of T. vulgare with slender straws tiller more than the thicker 

 strawed winter wheats. 



Tillering capacity is not only dependent upon the inherent vital 

 constitution of the species or variety concerned ; it is also greatly 

 influenced by internal qualities associated with difference in the size of 

 the grain from which the plants are raised. In experiments carried out 

 upon large and small grains which were sown in rows six inches apart, 

 and three inches asunder in the row, I found that large grains selected 

 from the ears of sixteen varieties of T. vulgare gave plants which pro- 

 duced an average of 8-1 stems per plant, while the small grains taken 

 from the same ears gave plants yielding only 4-4 straws each. Even 

 when the grains were grown at wider intervals, namely one foot apart 

 each way, the plants from the large grains produced an average of 14 

 straws each, those from the smaller grains only 10-6 per plant. 



Much of the increased luxuriance of the plants derived from large 

 grains is doubtless to be attributed to the abundant food supply in the 

 endosperm of such grains ; some of it, however, may be the result of 

 specific biological differences in the embryos of large as compared with 

 those of small grains, although these differences are probably not of much 

 magnitude in grains selected from the same ear. Nevertheless, the parti- 

 cular share in the variation of the tillering power which should be assigned 

 to each of these two causes can only be determined by further experiment. 



In addition to inherent qualities of the plants, other factors are con- 

 cerned in the tillering process. Profuse tillering is an index of natural 

 exuberant growth, and although the number, size, and vigour of the shoots 

 produced rests to some extent upon the hereditary qualities of the species, 

 variety, or form of wheat concerned, the branching and stem production 

 attained by any particular kind is due in largest measure to the action of 

 those external conditions which check or assist vegetative growth generally. 

 The question is one chiefly concerned with nutrition, and the tillering of 

 individual plants raised from grains taken from the same ear or spikelet 

 depends to a greater or lesser degree upon those external conditions which 

 favour or retard their nutritive functions. 



The temperature of the soil and air, the amount and distribution of 

 the rainfall, the intensity of the sunlight, and other climatic factors 

 connoted by the term " season " have a controlling influence upon the 

 tillering process. It is also greatly affected by the physical and chemical 

 condition of the soil, the density of " seeding " or the amount of space 

 allotted to each plant, and the date at which the grain is sown. 



For the most vigorous growth of the wheat plant comparatively dry 

 conditions are essential ; excessive moisture of the soil or atmosphere 

 greatly checks it and reduces tillering, especially when associated with low 

 temperature as in winter. 



