CYTOST IN THE PLANT WORLD 249 



the same fashion as the mucosal cells in contact with 

 mustard. As in the latter instance, the injury leads to 

 autolysis and the consequent liberation of cytost. This 

 substance in turn attacks adjacent cells, thereby giv- 

 ing rise to the "solution efifect" described by Wallace, 

 and those cells not exposed to too high a concentration 

 of the plant cytost are stimulated to division. 



Conceivably any other injury capable of liberating 

 cytost from the plant tissues should bring about a 

 similar situation. This is testified to by the well known 

 fact mentioned above, that the stimulus to intumes- 

 cence formation may take the form of abrasion, fun- 

 gus infection or chemical substances; although so far 

 as the writer has been able to ascertain the effects of 

 such stimuli have not been examined histologically 

 in a manner such as Wallace employed in his study 

 of the action of ethylene. This would appear to open 

 an interesting field of study and it is hoped that such 

 investigations will be carried out. 



The localized stimulation of growth which takes 

 place in the formation of intumescences is presum- 

 ably identical in nature with the various growth proc- 

 esses which accompany the tropistic bendings of 

 plants under various physical influences, and it may 

 be worth while to consider a few of these. The coil- 

 ing of the tendrils of phanerogams, the most sensitive 

 of all plant structures, has long been of interest to 

 botanists. The investigations of this curious phe- 

 nomenon by Darwin (1882) andPfeffer (1885) have 

 thrown considerable light upon the conditions pre- 

 requisite for such coiling. At the outset it was deter- 

 mined that tendrils are stimulated to depart from a 

 linear path of growth by contact with a solid body 



