THE LEAF 



183 



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

 apparent. The positions assumed vary in different plants, 



242 



243 



244 



Figs. 242-244. — Showing the movements of Amaranthus Palmeri: 242, 243, 

 position at sunrise and sunset (heliotropic) ; 244, night position (nj'ctitropic) half an 

 iiour 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. 



?4S 



24! 



FiG,q. 245-250. — Wild senna (Cassia tora), showing the nyctitropic adjustments 

 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. Lloj'd.) 



The very striking nyctitropic adjustments of the wild 

 senna {Cassia tora) photographed by Professor Francis 



