THE STATOCYSTS OF ROOTS 601 



starch, and the limits of the columella are therefore not so well defined. 

 The terminal that is,the oldest cells of the columella are either entirely 

 devoid of starch, or else contain starch-grains which no longer respond 

 to the action of gravity, but are irregularly distributed over the walls. 

 It is highly probable that these cells are in a senile state, and have lost 

 their faculty of perception. 



The number of cells included in the statolith-apparatus of the root 

 varies considerably in different species, and also according as the root 

 under consideration is a primary or a secondary one. Nemec estimates 

 the number of statocysts in an aerial root of Monstera deliciosa at 

 1800-1900. As a rule the sensory cells are far fewer in number. 

 Thus the main root of Boripa amphibia [Nasturtium amphibium] is 

 furnished with about 216 statocysts, while the lateral roots of the 

 same plant do not contain more than 96 of these cells. 



Statolith starch usually consists of rounded grains, about 2-7 jj. in 

 diameter ; the grains are generally of the compound type, but each is 

 made up of a comparatively small number of partial granules. They 

 arise in the ordinary way in the interior of leucoplasts, the stroma 

 of which persists as a thin envelope around the mature grain. The 

 starch-grains in the statocysts are sufficiently numerous to form 

 from one to three complete layers over the whole extent of the lower 

 wall of each cell. Thus every statocyst in the root-cap of Bo rip a 

 amphibia, contains about 26 starch-grains, a number sufficient to form 

 two complete layers, one above the other. 



The cytoplasm of statocysts is usually clear, hyaline and com- 

 paratively watery, so that the movements of the starch-grains are 

 interfered with as little as possible. The nuclei, which are fairly large, 

 may be unaffected by gravity, or they may respond like the statoliths, 

 in which case they usually come to rest at the upper less frequently 

 at the lower ends of the cells. The typical condition is illustrated by 

 Ceratopteris thalictroides, Hyacinthus orientalis, Allium, Cepa, Canna 

 indica, Salix viminalis, Phaseolus midtifloms, Cucurbita Pepo, Helianthus 

 animus, etc., the exceptional case by Equisctum arvense and Vicia Faba. 

 As long as the root is in the stable position, the cytoplasm is uniformly 

 distributed over the walls of the statocysts ; but, as Nemec has shown, 

 when the root is displaced, the distribution of cytoplasm in the sensory 

 cells also changes, the peripheral protoplasmic ] ayer becoming much 

 thicker and denser, and staining more deeply with haematoxyline on the 

 side which was lowermost, and hence covered with statoliths, in the stable 

 position. This rearrangement of the cytoplasm is interesting, if only 

 because it constitutes the first visible change produced in the sensory cells 

 by stimulation ; but it is improbable that the process forms a link in 

 the chain of stimulation which culminates in geotropic curvature. 



