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TEXTBOOK OF PLANT PHYSIOLOGY 



be more vigorous. Their functions of reproduction are thereby 

 depressed. Short-day plants are influenced in the same way by 

 the prolongation of the day to 16-18 hr. When cultivated in the 

 north, where the summer days are very long, short-day plants, 

 like millet, display great vegetative vigor, but flowering sets in late, 

 and the crop has no time to mature. Here again may be observed 

 the antagonism between vegetative and reproductive development, 

 which has been mentioned before. 



Fig. 146. — Development of Rudbcckia when exposed to a "long" day, A, and a 

 " short " day, B (after Gamer and Allard). 



A very profound influence is exerted by the duration of the day 

 on the development of tubers, bulbs, and other underground 

 storage organs. A long day chiefly promotes the development of 

 aerial organs, while a short day stimulates the formation of tubers 

 and bulbs. Many tropical plants characterized in their native 



