510 SENSORY SYSTEM 



It must be admitted that such amputation-experiments are not very 

 conclusive ; the infliction of a serious wound cannot fail to affect the 

 whole chain of stimulation, so that the interpretation of the results 

 becomes a matter of doubt. Nevertheless, experiments of this type have 

 a certain negative value, because their results have hitherto never come 

 into conflict with the statolith theory. 



2. A less drastic [and hence more reliable] type of experiment is 

 that which does not involve the actual excision of the statocysts, but 

 which aims at the removal of the statoliths by indirect means. For 

 this purpose Nemec embeds radicles of Vicia Faba in plaster of Paris, 

 the effect of such treatment being to inhibit growth completely, and to 

 bring about the solution of the starch contained in the root-cap. As a 

 rule, the statoliths disappear entirely when the roots have remained in 

 plaster of Paris for a week. If the roots are liberated at the end of 

 this period, they at once resume growth, but are found to be incapable 

 of curving geotropically until falling starch-grains are regenerated. This 

 experiment may reasonably be criticised on the ground that the prolonged 

 imprisonment of the root does not merely cause the statoliths to dis- 

 appear, but also probably paralyses the perceptive faculty of the 

 sensitive protoplasm for the time being. The following observation, 

 however, is less open to objection. Onions were allowed to germinate, 

 after having been stored for several years in a dry place. Vigorous 

 roots were put forth, which, during the first few days, responded to 

 hydrotropic, but not to geotropic stimulation: at this stage the root-cap 

 was invariably found to be devoid of starch-grains. After several days, 

 some of the roots exhibited geotropic curvature ; in all the cases examined, 

 these active roots contained falling starch in their root-caps. Other roots, 

 which remained permanently ageotropic, never formed any statoliths. 

 This experiment was repeated several years in succession, and always 

 gave the same result. 



Nemec is, therefore, undoubtedly justified in his assertion that the 

 correlation between the presence of falling starch on the one hand, and 

 the power of perceiving gravitational stimuli on the other, can scarcely 

 be considered accidental. 



A closely related series of experiments was carried out by the 

 author with stems in which the starch-sheath had been deprived of 

 starch, in common with all the other tissues owing to prolonged 

 exposure to low temperatures. Very suitable material presented itself 

 in the shape of plants of Linum perenne, L. usitatissimum, Capsella Bursa 

 pastoris, and Ruta graveolens, growing in the open during the mild and 

 comparatively snowless winter of 1901-2. The experiments performed 

 upon the two species of Linum may be dealt with first. Stems which 

 were completely devoid of starch were laid horizontally for 2-2 \ hours, 



