THE STATOCYSTS OF STEMS 



603 



grains at all, or else only such as always remain irregularly distributed. 

 This statement also applies to the geotropically insensitive roots of 

 certain saprophytes and parasites (Cuscuta, Orobanche, Pyrola), and to 

 various aquatic roots (Eichhornie, Pistia, Pontederia). In certain cases, 

 where the roots are at first ageotropic but subsequently become 

 positively geotropic (Lcontice Leontopetalum, L. Alberti, Festuea ovina, 

 Poo), the root-cap at first contains immovable starch-grains only, or 

 none at all ; the acquisition of geotropic sensitiveness coincides 

 with the appearance of falling starch-grains. Negatively geotropic 

 breathing-roots {Jussieua, Phoenix canariensis), again, are furnished with 

 typical statoliths. The aerial roots of epiphytic Orchids, which in most 

 cases are certainly ageotropic, contain no falling starch-grains. The 

 positively geotropic, nutritive aerial roots of Aroids, on the other 

 hand, are well provided with statoliths. The grasping roots of these 

 plants have been dealt with above. 



C. THE STATOCYSTS OF STEMS AND LEAVES. 



The author has shown that the statoliths of negatively geotropic 

 organs (stems, inflorescence-axes peduncles, pulvini) are usually con- 



Fig. 24S. 



Part of a T.S. through an iiiternode of Linum perenne (young enough to be capable 

 of geotropic curvature) which has been lying on its side for some time. The endo- 

 dermis contains large starch-grains (here stained with iodine), which are all resting 

 on the (physically) lower cell-walls. The outer cells of the phloem-rays likewise con- 

 tain falling starch-grains. 



