PHYSIOLOGY 265 



not only from the behaviour of the naked protoplasmic bodies of 

 spermatozoids, swarm-spores, plasmodia, and amoebee, but also from 

 the reactions manifested by walled cells and by whole organs, the 

 functions of which may be so disturbed by the action of mechanical 

 stimuli that death ensues. 



The almost universal irritability of vegetable protoplasm to 

 mechanical stimulation is utilised by a number of plants for the 

 production of movements which lead to their ultimate attachment to 

 the irritating body. Tendril-climbers, in particular, have developed 

 this irritability to contact stimuli as a means of attaching themselves 

 to supports ; and in that way are enabled to elevate their assimilating 

 and also their reproductive organs into more favourable situations. In 

 the case of twining plants which possess similar powers of climbing, 

 the process of elevation, as has already been shown, is accomplished 

 by means of the geotropic irritability of the stems themselves. In 

 the case of tendril-climbers, on the contrary, the attachment to the 

 support is effected, not by the main axis of the plant, but by lateral 

 organs of different morphological character. These may either main- 

 tain, at the same time, their normal character and functions, or, as is 

 usually the case, become modified and as typical tendrils serve solely 

 as climbing organs. The support operates, moreover, not as a 

 hindrance to a movement previously induced, as in the case of stem- 

 climbers, but itself produces curvature in the tendrils in consequence 

 of contact or friction. The contact of a tendril with a solid 



BODY ACTS UPON ITS GROWTH IN SUCH A WAY THAT THE ELONGATION 

 OF THE CONTACT SIDE IS ARRESTED, WHILE THAT OF THE OPPOSITE 



SIDE IS promoted. As a result of this, a sharp curvature of the 

 tendril ensues, which coils it about the support. The more slender 

 the tendrils and the stronger their growth, the more easily and 

 quickly this process occurs. Through the tendency of the curvature 

 to press the tendrils more and more firmly against the support, deep 

 impressions are often made by them upon yielding bodies, soft stems, 

 rubber tubing, etc. 



In the more typically developed tendrils the curvature does not 

 remain restricted to the portions directly subjected to the action of 

 the contact stimulus. Apart from the fact that, in the act of coiling, 

 new portions of the tendrils are being continually brought into contact 

 with the support and so acted upon by the stimulus, the stimulation to 

 curvature is also transferred to the portions of the tendril not in 

 contact with the support. Through the action of the propagated 

 stimulus, not only is the free apex of the tendril turned more quickly 

 around the support, but a tendency to curvature is imparted to the 

 portion of the tendril between the support and the parent shoot. As 

 it extends between two fixed points, this tendency causes it to coil 

 spirally, like a corkscrew. With the spiral coiling, a torsion is 

 produced, and, on account of the fixed position of the two end 



