420 



PLANT PHYSIOLOGY 



engaged in working out its details, and it is very probable that 

 sooner or later it will undergo certain changes. But as it is, it 

 represents a great step forward on the way toward ascertaining 

 the laws of the development of plants and provides useful 

 methods for controlling development in the desired direction. 



The practical application of the methods of yarovisation is 

 extremely diverse. Shortening the vegetative period in cereal 



Fig. 132. — Millet plants from non-yarovised seed, A, and plants from yarovised 



seed, B, of same age. 



crops is one of the most important means of escaping drought, 

 especially in regions where drought occurs chiefly in the latter 

 part of the summer, as in the north central Great Plains and in 

 South and Southeast Russia, where even in relatively moist 

 years the soil is completely dried towards autumn. In such 

 regions, it is possible now to sow valuable late-wheat varieties. 

 Thus, the vegetative period is shortened by means of yarovisa- 

 tion, and they escape the late drought; while before the elabora- 

 tion of the method of yarovisation, it was only the less valuable 

 early varieties that could be sown in these regions. 



