500 PHYSIOLOGY OF GROWTH. 



phenomenon, since the spirals are of course formed in the free 

 parts of the tendrils, not in the parts directly touched. 



With reference to the mechanics of tendril movements, this 

 much is known with certainty, that when a tendril has been 

 stimulated by contact, and curvatures have been effected, the 

 turgor-expansion of the cells of the now concave side is less than 

 that of the cells of the now convex side. This preliminary differ- 

 ence in turgor-expansion, called into existence by the contact 

 stimulus, then further leads to a difference in the growth of the 

 cells of the concave and convex sides of the tendril. The cells of 

 the latter grow more actively than those of the former, and thus 

 the curvatures induced by the stimulus become fixed. By means 

 of the plasmolytic method (see 59) we are enabled to determine 

 the share taken in the production of the tendril curvatures by 

 turgor-expansion on the one hand and the growth of the cells on 

 the other, and it is instructive to make such experiments. The 

 method is to stimulate the tendrils slightly or strongly, and then, 

 when more or less considerable curvatures have taken place, cut 

 them off and lay them at once in a 20 per cent, solution of com- 

 mon salt. If, under plasmolysis, the curved tendrils completely 

 straighten again, the curvature resulting from the stimulus of 

 contact was only occasioned by a difference in the turgor-expan- 

 sion in the cells on the concave and convex sides of the tendril. 

 If, on the other hand, complete straightening is not effected by 

 plasmolysis, the participation of growth in the development of 

 the spirals is demonstrated. I have stimulated Sicyos tendrils, 

 and, after they had developed }, f , or 1J turns, subjected them to 

 plasmolysis. The two first tendrils soon straightened completely ; 

 the last retained in the salt solution J of a turn. 3 



The tendrils of the Cucurbitacese are very irritable only at their 

 tips, as was found to be the case with Sicyos tendrils ; the irrita- 

 bility gradually falls off as we proceed towards their base. This 

 is undoubtedly related to the fact, of the truth of which I was 

 satisfied from the descriptions of 0. Miiller, 4 that the base of the 

 tendrils in Cucurbitaceae is radial in structure, while the nearer 

 we approach the highly sensitive tips of the tendrils the more 

 pronounced becomes their dorsiventrality of structure. We pre- 

 pare, e.g., a large number of sections from a tendril of Bryonia 

 dioica. At the base the tendril is completely or approximately 

 radial in structure. We perceive the vascular bundles, regularly 

 disposed in the pith, a closed ring of sclerenchyma, the elements 



