BIOLOGICAL ADAPTATIONS OF TENDRILS. 



667 



means brought wiihin tlie 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 



^-^^^^^ 



-r'' ^-_ ^- 



-^ )); 



FIG. 378,— Upper portion of the end of a climbing shoot of the Virginian Creeper [Ampelopsis heiUtacea). h a tendril 

 which has coiled itself in the ordinary manner round a nail ; a c 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 {Pisiim according to Darwin), in others a feeble positive helio- 

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

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



