TENDRILS 



But these leaves are not to be compared as regards perfec- 

 tion of mechanism with the tendrils by means of which plants 

 climb. These tendrils are thin, flexible, twining threads, 

 which may be formed by the modification of whole leaves, 

 in other cases of leaflets, or sometimes of branches. Sweet 

 Peas, Vetches, Passion-flowers, Vines, and many other plants 

 possess them. 



They are like twining plants in the way in which they 

 revolve or twine so as to wrap themselves round anything 

 which they touch. They move much faster than twining 

 plants. A Cobaea tendril only takes twenty-five minutes to 

 make a complete turn, Passion-flowers take from half to 

 three-quarters of an hour, and the Vine tendril takes a little 

 over an hour to make one complete turn. 



But in one way they diff'er altogether, for they are sensitive 

 to contact. If tickled, they contract and embrace closely 

 the object which is touching them. They show a most 

 extraordinary sensibility and sensitiveness. 



As a matter of fact, these tendrils have a finer sense of 

 touch and a much more delicate feeling of weight than any 

 human being. They detect the weight of twenty-seven 

 inches of a spider^s thread. 



It is, however, best to explain what happens. A half- 

 grown curved tendril of the Passion-flower is perhaps the 

 most interesting to experiment with, but any sort of tendril 

 does quite well. If one very gently rubs the inner or concave 

 side of its little hook, then in a very few minutes, or even 

 seconds, the tendril distinctly curves. If this has happened 

 naturally, as when for instance it has been rubbing upon a 

 pea-stick, this curve makes it curl round the stick, and the 

 more it touches the more it curls, until the whole tendril is 

 wrapped round the support. 



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