Chap. III. LEGUMINOS^. 115 



curved in harmony together, owing to inequality of 



age. 



Dutrochet made no observations on the sensitiveness 

 of the tendrils. These, whilst young and about an inch 

 in length with the leaflets on the petiole only partially 

 expanded, are highly sensitive; a single light touch 

 with a twig on the inferior or concave surface near the 

 tip caused* them to bend quickly, as did occasionally 

 a loop of thread weighing one-seventh of a grain 

 (9*25 mg.). The upper or convex surface is barely or 

 not at all sensitive. Tendrils, after bending from a 

 touch, straighten themselves in about two hours, and 

 are then ready to act again. As soon as they begin 

 to grow old, the extremities of their two or three pairs 

 of branches become hooked, and they then appear to 

 form an excellent grappling instrument; but this is 

 not the case. For at this period they have generally 

 quite lost their sensitiveness ; and when hooked on to 

 twigs, some were not at all affected, and others required 

 from 18 hrs. to 24 hrs. before clasping such twigs; 

 nevertheless, they were able to utilise the last vestige 

 of irritability owing to their extremities being hooked. 

 Ultimately the lateral branches contract spirally, but 

 not the middle or main stem. 



Lathyrus aphaca. This plant is destitute of leaves, 

 except during a very early age, these being replaced 

 by tendrils, and the leaves themselves by large stipules. 

 It might therefore have been expected that the ten- 

 drils would have been highly organized, but this is 

 not so. They are moderately long, thin, and un 



