Cuap. IV. SUMMARY. 175 
revolve and after they have sunk downwards; in this 
position, even if they were able to seize an object, such 
power would be of no service in supporting the stem. 
It is a rare circumstance thus to detect any super- 
fluity or imperfection in the action of tendrils—organs 
which are so excellently adapted for the functions 
which-they have to perform; but we see that they are 
not always perfect, and it would be rash to assume 
that any existing tendril has reached the utmost limit 
of perfection. 
Some tendrils have their revolving motion accelerated 
or retarded, in moving to or from the light; others, 
as with the Pea, seem indifferent to its action; others 
move steadily from the light to the dark, and this aids 
them in an important manner in finding a support. 
For instance, the tendrils of Bignonia capreolata bend 
from the light to the dark as truly as a wind-vane from 
the wind. Inthe Eccremocarpus the extremities alone 
twist and turn about so as to bring their finer branches 
and hooks into close contact with any dark surface, or 
into crevices and holes. 
A short time after a tendril has caught a support, 
it contracts with some rare exceptions into a spire; 
but the manner of contraction and the several important 
advantages thus gained have been discussed so lately, 
that nothing need here be repeated on the subject. 
Tendrils soon after catching a support grow much 
stronger and thisker, and sometimes more durable to a 
wonderful degree; and this shows how much their 
internal tissues must be changed. Occasionally it is 
