174 TENDRIL-BEARERS. Cuar. IV. 
with a stick, do they not, like twining plants, spirally 
wind round it? One reason may be that they are in 
most cases so flexible and thin, that when brought 
into contact with any object, they would almost 
certainly yield and be dragged onwards by the revoly- 
ing movement. Moreover, the sensitive extremities 
have no revolving power as far as I have observed, 
and could not by this means curl round a support. 
With twining plants, on the other hand, the extremity 
spontaneously bends more than any other part; and 
this is of high importance for the ascent of the plant, 
as may be seen on a windy day. It is, however, possible 
that the slow movement of the basal and stiffer parts 
of certain tendrils, which wind round sticks placed in 
their path, may be.analogous to that of twining plants. 
But I hardly attended sufficiently to this point, and it 
would have been difficult to distinguish between a 
movement due to extremely dull irritability, from the 
arrestment of the lower part, whilst the upper part 
continued to move onwards. 
Tendrils which are only three-fourths grown, and 
perhaps even at an earlier age, but not whilst extremely 
young, have the power of revolving and of grasping 
any object which they touch. These two capacities 
“are generally acquired at about the same period, and 
both fail when the tendril is full grown. But in 
Cobea and Passiflora punctata the tendrils begin to 
revolve in a useless manner, before they have become 
sensitive. In the Echinocystis they retain their 
sensitiveness for some time after they have ceased to 
