The Roots of the Wheat Plant. 



179 



causing the starting: of new roots, whilst the older roots branch 

 into fibres and fibrils : still farther removed from the centre of 



Fig. 2. Fig. 1. 



Diagram 5. — a, a, a. Buds starting from the axilla of the root-leaves, which ate turned back 

 to show them. 



growth, the older rootlets providing for the necessities of the 

 primitive plants, whilst the newer ones take care of the more 

 recent buds. 



This process of tillering is much interfered with by the follow- 

 ing causes. A too thick sowing, like thick planting of trees, 

 causes the plants to grow up thin and emaciated, and thus the 

 central axis is elongated ; in which case the lateral buds are not 

 usually brought to perfection, or, if they do grow, it is only thin 

 and irregularly, and without a disposition to rebranch ; for it 

 must be remembered that when lateral branches are strong they 

 in turn give off others. 



Tlie thin mode of growth is induced in even thin sowing with 

 a very mild autumn and winter, when the wheat is called winter- 

 ])n)U(l. Here, then, the winter has not succeeded in sufficiently 

 crij)pling the upward growth of the plant ; that is, its develop- 

 ment has not been arrested, and this explains the principle upon 

 which a liard winter is often beneficial to the wheat crop, and 

 which has hitherto been attributed to slucrs and insects bein<x 

 killed by tlie frost. Upon tliis point, however, it may be re- 

 marked, that the winter of 1851-5 was one of the severest of 

 late years, yet insect life in the siiinnier of 1855 was more 



N 2 



