﻿the Physiology of Tendrils 71 



ancestral climbers to avoid this injury, and at the same time climb 

 more effectively. The development of the irritability to contact 

 in the extremities of the leaf and the transformation of such mem- 

 bers into filiform organs would be a natural consequence, and an 

 inevitable one in species bearing large or extended leaves, such as 

 the one under consideration. Furthermore, the general phylogeny 

 of Entada would not indicate that it has been a twiner at any time 

 in its existence. 



A consideration of the features of the irritability of the tendril 

 leads to the conclusion that the efficiency of the tendril is by no 

 means dependent upon the degree of dorsiventrality exhibited. 

 The isodiametric tendrils of Entada are quite as effective in grasp- 

 ing supports and exhibit as great a degree of delicacy of sensorial 

 action as any organs yet examined, and they show no tendency 

 toward dorsiventrality. 



Dorsiventrality is induced only by pressure of the support 

 where it is of some benefit in securing a firmer hold. The delicacy 

 of reaction depends more upon centralization and concentration of 

 the woody cylinder, a fact to which I have previously called at- 

 tention. The lack of collenchyma in the tendrils of Entada is 

 probably due to the almost entire absence of torsional strains 

 during the curvature of the tendril. The collenchyma sheath of 

 many tendrils is doubtless to resist the effects of torsional strain. 

 Attention is to be called here to the fact that, in the tendrils of 

 Entada, nearly the entire length of the tendril engages the support 

 in a single continuous spiral, and free coiling forms only part of a 

 circle in the basal portion of the organ. 



lanism of curvature is seen to resemble that of ten- 



mec 



drils of Passiflora and the roots of Zea, in which the mechanical 

 elements are centralized and in which the motor tissue occupies a 

 relatively great portion of the cross section. Curvature is effected 

 by the contraction of the cells of the side becoming concave, a 

 condition demanded by the rapidity of reaction. 



The work recorded in this paper was largely performed in- or 

 near the botanical gardens at Castleton and Bath in Jamaica, m 

 the summer of 1897, and the writer is indebted to Hon. Wm. 



