BIOLOGICAL ADAPTATIONS OF TENDRILS. 



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means brought within the area swept by the tendrils, almost certainly comes in contact 

 with one. The apex of the shoot bearing the tendrils usually describes elliptical ascend- 

 ing spirals, the course of which is completed in from i to 5 hours. As with twining 



FIG, 37B.— Upper portion of the end of a climbing shoot of the Virginian Creeper {Ampelopsis hederaaa), b a tendril 

 which has coiled itself in the ordinary manner round a nail ; ac tendrils which have become fixed to the wall by means of 

 cushion-like outgrowths or clasping organs ; d a tendril which is still nutating — its tips are groping about on the wall, but 

 are still devoid of clasping organs ; e young tendrils. 



Stems so also with tendrils, a pronounced positive heliotropism would often carry them 

 away from the support, and would therefore be injurious. Some in fact appear to be 

 not heliotropic at all {Pisum according to Darwin), in others a feeble positive helio- 

 tropism makes itself evident by the fact that the circular nutating movement takes 

 place more quickly towards the light than away from it. Some tendrils, particularly 



