Twining of TfiNr>liiLS 289 



of explanation of twining movements is accentuated by a 

 peculiarity in the response of tendrils which is extremely 

 puzzling. This anomaly was observed by Fitting in tendrils 

 which are sensitive on the under side : 



"If a small part of the upper side and at the same 

 time the whole of the under side be stimulated, curvature 

 takes place only at the places on the under side which lie 

 opposite to the unstimulated regions of the upper side. The 

 sensitiveness to contact is thus as well developed on the 

 upper side as on the under side, and the difference between 

 the two sides lies in the fact that while stimulation of the 

 under side induces curvature, stimulation of the upper side 

 induces no visible result, or simply inhibits curvature on 

 the under side, according to circumstances."* 



Here then we have the inexplicable phenomenon of a 

 particular tissue, itself incapable of response, yet arresting 

 the movement in a neighbouring tissue. 



The problem before us may be thus stated : Is the move- 

 ment of the tendril due to certain specific sensibility of the 

 organ, on account of which its reactions are characteristically 

 different from other tropic movements ? Or, does the twining 

 of tendril come under the law of tropic curvature that has 

 been established, namely that it is brought about by the 

 contraction of the directly stimulated proximal side, and the 

 expansion of the indirectly stimulated distal side ? 



I shall now describe ray investigations on the effects of 

 direct and indirect stimulus on the growth of tendril ; I 



* Jost— /6t(/— p. 490. 



