422 



PLANT PHYSIOLOGY 



in yield of yarovised plants may be observed not only in espe- 

 cially cold or droughty regions but everywhere. Mass experi- 

 ments in yarovisation carried out all over Russia in the collective 

 farms in 1934 gave an average increase of yarovised wheat as 



Fig. 133. — Development of short-day plants — millet. On the right, plants 

 grown in 9 to 12 hr. of daylight per day. Left, plants grown in 18 hr. daylight 

 per day. Both sets are the same number of days old. 



compared with those not yarovised of about 1.13 cwt. per 

 hectare; in some cases, the increase attained 2 to 3 and even as 

 high as 9 cwt. 



97. Influence of Length of Day on the Development of Plants. 

 Photoperiodism. — Garner and Allard's investigations, which have 



