Cuap. 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 
species have the power of revolving. The Vine 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 of Bignonia littoralis 
move much slower than the internodes. Generally, 
