184 



DIAHELIOTROPISM. 



[CH. VII 



heliotropic curvature to occur, the contrast between the 

 capped seedlings, which remain upright, and the others, 

 which are sharply bent towards the light, is striking. 



SECTION D. Diaheliotropism, Diageotropism, 



Epinasty, Nutation of Epicotyls. 

 (216) Diaheliotropism or transverse heliotropism 1 . 



Before proceeding to experiment in this subject, it is 

 well to study the positions naturally assumed by leaves 



FIG. 35. Exp. 216. 



when obliquely illuminated. For this purpose plants 

 with decussate leaves are useful, e.g. Lamium album, 



1 Frank, Naturliche wagerechte Eichtung von Pflanzentheilcn (Leipzig), 

 1870. 



