Chap. 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. 

 Foi instance, the tendrils of Bignonia capreolata bend 

 from the light to the dark as truly as a wind- vane from 

 the wind. In the 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 tb^ker, and sometimes more durable to a 

 wonderful degree; and this shows how much their 

 internal tissues must be changed. Occasionally it is 



