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, the internodes and tendrils revolve together at the same
rate; in Cissus, Cobaea, and most Passiflorae, the tendrils alone
revolve; in other cases, as with Lathyrus aphaca, only the internodes
move, carrying with them the motionless tendrils; and, lastly (and
this is the fourth possible case), neither internodes nor tendrils
spontaneously revolve, as with Lathyrus grandiflorus and Ampelopsis.
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