EXPERIMENTAL BASIS OF STATOLITH THEORY 609 



geotropic curvature takes place. Although these starch-grains are not 

 mobile, they may very well act as statoliths. 



Since Fungi never form starch, other bodies of relatively high (or 

 low) specific gravity must serve as statoliths in that group. This point 

 still awaits investigation. In any case it is quite possible, that percep- 

 tion of gravitational stimuli does not always take place precisely in the 

 same manner among Fungi and Algae, as it does in the Higher Plants. 



D. EXPERIMENTAL OBSERVATIONS REGARDING THE DEPENDENCE OF 

 GEOTROPIC SENSITIVENESS UPON THE PRESENCE OF STATOLITHS. 



The statolith theory has been subjected to the test of experiment 

 in a variety of ways, so far without the discovery of a single fact which 

 is irreconcilable with the theory ; as a matter of fact, a whole number 

 of data have already come to light which furnish more or less conclusive 

 evidence in its favour. 



1. Mention may first be made of certain amputation-experiments 

 performed by Nemec and by the author. All these experiments were 

 arranged, so as to test whether a root or stem remains geotropically 

 sensitive after its statocysts have been removed. Nemec found, that 

 a root is incapable of curving geotropically for a long time after its 

 root-cap has been cut off, but that it returns to its normal condition 

 when falling starch-grains reappear in the wound-callus. The temporary 

 loss of the perceptive or reactive capacity is not, as might be supposed, 

 merely due to shock ; for geotropic curvature is not interfered with to 

 the same extent, if several transverse incisions are made in the root-tip 

 which collectively produce a wounded surface equal to that created by 

 the removal of the root-cap. Nemec tried various modifications of this 

 experiment, and always met with the same result ; he therefore con- 

 cludes that geotropic sensitiveness of roots is dependent upon the 

 presence (ab initio, or as a result of regeneration) of falling starch- 

 grains. Analogous amputations have been carried out by the author 

 upon stems. In the Commelynaceae, it is only the more or less distinctly 

 pulvinoid basal region of each internode that is capable of perceiving 

 gravitational stimuli and of executing geotropic curvatures. If the 

 sub-epidermal collenchyma-strands and the greater part of the cortical 

 parenchyma be removed from a node of Traclcscantia virginica, while 

 the starch-sheath and one or two of the immediately adjacent cortical 

 layers are left intact, the geotropic reactivity of the organ is found to 

 be almost as energetic as that of an uninjured node. If, however, the 

 remainder of the cortex, including the starch-sheath, is likewise removed, 

 the geotropic capacity is completely lost ; a feeble power of curvature is 

 retained in the latter case, if, as sometimes happens, falling starch is 

 present in the pith as well as in the endodermis. 



2Q 



