THE LEAF 



183 



leaves, too slight to attract attention otherwise, will be made 

 apparent. The positions assumed vary in different plants, 



242 



244 



FIGS. 242-244. Showing the movements of Amaranthus Pcdmeri: 242, 243, 

 position at sunrise and sunset (heliotropic) ; 244, night position (nyctitropic) half an 

 hour after sunset. (From photographs by Prof. F. E. Lloyd.) 



and even in the parts of the same compound leaf; in the 

 kidney bean, for instance, the common petiole turns up at 

 night, while the individual leaflets turn down. One of the 

 common pigweeds (Amaranthus Palmeri, Figs. 242-244) is 

 heliotropic in the day time and nyctitropic at night. 



246 



247 





i*% 



24S 



249 



FIGS. 245-250. Wild senna (Cassia occidentalis), showing the nyctitropic ad- 

 justments of its leaves. The upper figures show their horizontal arrangement; 

 those below, the vertical : 245, 248, position of the leaves at 9 A.M. ; 246, 249, at 

 3 P.M. ; 247, 250, at 6.30 P.M. (From photographs by Prof. F. E. Lloyd.) 



The very striking nyctitropic adjustments of the wild 

 senna (Cassia occidentalis) photographed by Professor Francis 



