Chap. IV. SUMMARY. 169 



direction ; but in both cases the self-twisting is 

 avoided. 



Summary on the Nature and Action of Tendrils. 



With the majority of tendril-bearing plants the young 

 internodes revolve in more or less broad ellipses, like 

 those made by twining plants ; but the figures de- 

 scribed, when carefully traced, generally form irregular 

 ellipsoidal spires. The rate of revolution varies from 

 one to five hours in different species, and consequently 

 is in some cases more rapid than with any twining 

 plant, and is never so slow as with those many twiners 

 which take more than five hours for each revolution. 

 The direction is variable even in the same individual 

 plant. In Passiflora, the internodes of only one 

 sj)ecies have the power of revolving. The Yine is 

 the weakest revolver observed by me, apparently 

 exhibiting only a trace of a former power. In the 

 Eccremocarpus the movement is interrupted by many 

 long pauses. Very few tendril-bearing plants can 

 spirally twine up an upright stick. Although the 

 power of twining has generally been lost, either from 

 the stiffness or shortness of the internodes, from the size 

 of the leaves, or from some other unknown cause, the 

 revolving movement of the stem serves to bring the 

 tendrils into contact with surrounding objects. 



The tendrils themselves also spontaneously revolve. 

 The movement begins whilst the tendril is young, and 

 is at first slow. The mature tendrils oiBignonia littoralis 

 move much slower than the internodes. Generally, 



