376 MacDougal . — The Mechanism of 
water directed against a tendril would not cause a reaction, 
yet if some substance in the form of fine powder were sus- 
pended in the water, the repeated impact of these particles 
induced reaction, although their diameter was only -04 mm., and 
their weight must have been only a fraction of that used by 
Darwin. In further experiments by Pfeffer, a rider weighing 
•00025 mg. placed gently upon a tendril gave no reaction, but 
when it was moved by the wind, curvature resulted (XVII). 
It has come under the author’s observation that a spider’s 
thread, 43 cm. long, suspended above a tendril of Echinocystis , 
caused such reaction that the tendril coiled around and 
fastened to it. It will be found that a reaction in some of the 
more highly irritable tendrils of the Passifloraceae may be 
obtained in twenty-five seconds, while Muller (XIV) noted 
a curvature in the tendrils of Cyclanthera five seconds after 
stimulation. In many forms the latent period may extend 
over sixty to one hundred minutes. 
The forces which act as stimuli upon the different types 
of tendrils sensitive to contact, appear to offer no means of 
distinction of the mechanism by which the reaction is accom- 
plished. In general it may be said that clasping tendrils 
are sensitive to contact or repeated impact of solid bodies, 
but not to static pressure, or to shock such as that given 
by jarring the soil in which the plant stands, and to which 
Mimosa responds so readily, a generalization first stated by 
Pfeffer (XVIII, pp. 517-524). The distinct and important 
mechanical, anatomical, and physiological conditions to be 
found among tendrils which apparently react in a similar 
manner to identical stimuli, does not warrant the assumption 
that the reactions in all classes of tendrils are identical. Not 
only does this apply to the actual mechanism of movement, 
but also to that of the transmission of the effects of stimula- 
tion. Thus Pfeffer (XVIII) has found that the excision of 
certain tendrils, viz., Sicyos angulatus and Passijlora gracilis , 
was followed by the exudation of a drop of water from the 
exercised surfaces, a result which I have also obtained in all 
species of Passijlora and Cucurbitaceae examined. On the 
