THE LEAF 183 
leaves, too slight to attract attention otherwise, will be made 
apparent. The positions assumed vary in different plants, 
242 243 244 
Fics. 242-244.—-Showing the movements of Amaranthus Palmeri: 242, 2438, 
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 
wing | ~o 
248 249 250 
Fies. 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 
