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TEXTBOOK OF BOTANY 



The greater variability in behavior of plants exposed to intermediate 

 day-lengths near their critical photoperiod includes not only the vari- 

 ability in the initiation of flowers, but also the variabilitv in the further 

 development of flowers and fruits and the processes involved in seed 

 formation. Changes in vegetative structures, such as growth in height 





ism 



Fig. 148. 



Fig. 149. 



Fig. 148, the plant on the right, an apple seedling that grew more rapidly with 

 10 hours' daily illumination than the control plant on the left with a full day's 

 illumination. In contrast, the maple seedlings {Acer negundo) on the left in Fig. 

 149 were dwarfed and forced into dormancy by shortening the illumination period 

 to 10 hours, while the plant exposed for the full length of day grew rapidly. The 

 photograph of the apples was made July 13 and that of the maples September 22 

 by W. W. Garner and H. A. Allard. Photo from U. S. Dept. Agric. 



