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General Botany 



Long day Short day 



Fig. ii8. The effect of long and short days on the evening 

 primrose. Both plants were brought into the greenhouse in No- 

 vember. The one at the left received, in addition to daylight, 

 illumination from an electric light from sunset to midnight for 

 about two months. The one at the right was kept under; ex- 

 actly the same conditions, except that it received only the nat- 

 ural winter daylight. This is a typical long-day plant, in nature 

 flowering when the days are long. (Garner and Allard. U.S.D.A.) 



Wheat has been ripened at 57° north latitude, and immense yields 

 of hay are produced at 60° north latitude along the coast of Alaska. 

 These large crops are made possible by the continuous or long 

 daily period of sunhght during the growing season. 



Medium light favors the growth of vegetative structures. 

 Attention has already been called to the fact that leaves and many 

 kinds of stems attain their largest size in partial shade. 



