Curvature of Tendrils . 375 
may occur during curvature, and may amount to one-third 
of the original length of the organ ; and furthermore admits 
that in consequence of the relaxation and loss of water of 
the parenchyma of the concave side, the elastic contraction 
of the cell- walls may co-operate in producing curvature or 
coiling. 
The mechanism by which the attachment of tendrils and 
other climbing organs to supports is accomplished, has under- 
gone widely different methods and degrees of development in 
different groups. In some instances, attachment is made by 
means of disc-like suckers or outgrowths adapted to the 
surface to which adhesion is desirable. In others, the same 
purpose is accomplished by means of mucilage-masses secreted 
by groups of specialized cells. In others, attachment is by 
means of curvatures which more or less encircle the support. 
In the last-named group the tendrils may possess the power 
of contact-irritability over almost their entire surface, and be 
able to curve in any direction ; or the seat of irritability may 
lie on one side alone, which always forms the concavity of the 
curvature. After attachment to a support, the tendril 
generally throws its free portion into a number of loose coils, 
which results in shortening the distance between the shoot 
and support. In this manner as each internode successively 
develops, it is drawn up and fastened to the support. In 
order that this fixation may be effected economically, it is 
important that exact correlations should exist between the 
activities of the tendril and those of the shoot. It will be 
found, therefore, that rapidly growing plants are, in the 
majority of instances, furnished with tendrils of greatest sensi- 
bility and rapidity of reaction to contact, and conjointly the 
consequent free coiling of the tendril will be rapid and strong 
because of this power of rapid growth extended to the tendril. 
As examples of the smallness of stimuli which may cause 
a reaction may be mentioned the experiments of Charles 
Darwin (I, p. 171), in which it was found that a tendril of 
P as siflor a gracilis responded when a weight of 1-23 mg. was 
gently laid upon it. Pfeffer found that while a stream of 
