116 



The Plant World. 



he shows further that the degree of retardation of growth of 

 the hypocotyl is dependent on the intensity of the light, and also 

 on whether the whole or a part of the seedling is exposed to it. 

 Since this retardation takes place following illumination of the 

 cotyledon, the conclusion follows that an influence is transmitted 

 downward to the hypocotyl. It appears, however, that a 

 transmission of such an influence in the reverse direction does 

 not take place, since if the lower part only of the hypocotyl is 

 illuminated, growth of the upper part is not retarded. That the 

 hypocotyl is itself sensitive to light, even if not phototropic, 

 was shown by cutting off the cotyledon, after which growth was 

 resumed in darkness but not in light. From this and other ex- 

 periments, it is shown that in the several species of grasses 

 employed a localized phototropic sensitiveness does not justify 

 the assumption of a corresponding localization of light perception. 



It is of interest to note that, after these many years of ex- 

 tended investigation of the phenomena of irritability in plants, 

 there is still entire lack of agreement concerning some of the most 

 fundamental matters. Fitting, the writer just quoted, in his 

 studies of the transmission of stimulus, reaches the conclusion 

 "that the view that geoperception of the root is located only 

 in the root-tip is not proven"; while Cholodny, in a paper on 

 distribution of geotropic sensitiveness, reaches results that "go 

 to confirm the Darwinian theory of localization of geotropic 

 sensitiveness in the root-tip." 



Similarly the good old question of the ascending current in 

 plants, and what causes it, still holds a place in current litera- 

 ture. Janse, in the Jahrb. f. wissenschaftl. Botanik, argues 

 that molecular action, as manifested in capillarity, imbibition, 

 and cohesion, are incapable of setting up movement of water. 

 Transpiration from the leaves and forces at work in the roots 

 play the principal role. These conclusions, based on a course 

 of reasoning, recall some of the earlier discussions of the subject, 

 and lead one to seriously raise the question as to how much 

 real progress has yet been made in the elucidation of this diffi- 

 cult problem. 



