EXPERIMENTAL BASIS OF STATOLITH THEORY Cll 



at a temperature of 17C.-20'C and were afterwards rotated upon the 

 klinostat ; not the slightest geotropic curvature could be detected. If 

 the experimental shoots were then kept in the warm atmosphere of the 

 laboratory for 24 hours, statoliths reappeared in the starch-sheath ; 

 when this had occurred, a sojourn of 2-2 h hours in the horizontal 

 position resulted in typical geotropic curvature after a few hours' 

 subsequent rotation on the klinostat. It might, of course, be objected 

 that the long exposure to a low temperature had resulted in a disturbance 

 of the sensitive protoplasm, of the mechanism of curvature, or of some 

 other link in the complicated chain of stimulation ; this argument is 

 partially disposed of by the fact, that shoots in which the statoliths 

 had been regenerated under the influence of the warmth of the labora- 

 tory, responded at once to geotropic stimulation after a second period of 

 exposure to temperatures between 2*5 C. and 5 C, lasting 17 hours. 

 A few of the young inflorescence-axes of Capsella Bursa pastoris had 

 either not become entirely deprived of starch through exposure to low 

 temperatures, or else had regenerated their statoliths with unusual 

 rapidity ; these shoots displayed geotropic curvature in the course of 

 a few hours, when subjected to higher temperatures, in contradistinction 

 to control specimens entirely deprived of starch, which showed no trace 

 of curvature under similar conditions. In the case of Buta graveolens, 

 the reappearance of statoliths was a slow process, occupying as much as 

 five days ; geotropic sensitiveness remained in abeyance for the same 

 period. Shoots which are normally negatively geotropic, therefore, lose 

 their capacity for geotropic response, if the starch-sheath becomes 

 deprived of its starch-grains ; this behaviour seems inexplicable, except 

 on the assumption that the sensitive ectoplast of a statocyst cannot 

 be effectively stimulated in the absence of the falling starch-grains which 

 act as statoliths. 



3. Further important evidence in favour of the statolith-theory 

 is furnished by the vibration experiments which have been carried 

 out by the author and by F. Darwin. 312 The argument is roughly as 

 follows : If the effective stimulus actually consists in the pressure 

 of the falling starch-grains upon the ectoplast into which they sink, the 

 intensity of stimulation should be increased, when the deformation 

 of the protoplasm is accelerated by the substitution of a rapid succes- 

 sion of vertical impacts in place of the single blow which each statolith 

 inflicts under ordinary conditions. In the author's experiments, 

 peduncles, inflorescence-axes or roots were placed horizontally and 

 subjected to a series of shocks, or to rapid vibration, with the aid of 

 special apparatus. The number of vibrations varied between five 

 and fifteen per second, while their amplitude generally amounted only 

 to fractions of a millimetre. The effect of this treatment was a more or 



