102 MR. DABWIK O^ CLIMBING PLAINTS. 



tlie EcMnocystis they retained their sensitiveness for some time 

 after they had ceased revolving and had drooped downwards ; in 

 this position, ^ven if they should seize any object, they could be 

 of little or no use in supporting the stem. It is a rare circum- 

 stance thus to be able to detect any imperfection or superfluity 

 in tendrils — organs which are so admirably adapted for the func- 

 tions which they have to perform ; but we see that they are not 

 always absolutely 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 and 

 retarded in moving to and from the light; others, as with the 

 Pea, seem indifferent to its action ; others move from the light to 

 the dark, and this aids them in an important manner in finding a 



support. 



tendrils 



win 



In the Gohcea and 

 Hccremocarpus the extremities alone twist and turn about, so as 

 to bring their finer branches and hooks into close contact with 

 any surface, or into dark crevices and holes. This latter movement 

 is one of the best adapted exhibited by tendrils. 



A short time after a tendril (with some rare exceptions) has 

 caught a support, it contracts spirally ; but the manner of con- 

 traction and the several important advantages thus gained have 

 been so lately discussed, that nothing need be here said on the 

 subject. Again, tendrils soon after catching a support grow 

 much stronger and thicker, and sometimes in a wonderful degree 

 durable ; and all this shows how much their internal tissues must 

 change. Tendrils which have caught nothing soon shrink and 

 wither ; in some species of Bignonia they disarticulate and fall oif 

 like leaves in autumn. 



Any one who did not closely study tendrils of various kinds 

 would probably infer that their action would always be uniform. 

 This is the case wdth most kinds of tendrils, of which the extre- 

 mities simply curl round objects of any moderate degree of thick- 

 ness, and of various shapes or natures. But JBignonia shows us 

 what diversity of action there may be in the tendrils of even 

 closely allied species. In all the nine species of this genus ob- 

 served by me the young internodes revolved vigorously ; as did the 

 petioles of nearly all, but in very unequal degrees ; in three of the 

 species the petioles were sensitive to contact ; the tendrils of all 

 are sensitive to contact, and likewise revolve, but in some of the 

 species in a very feeble manner. In the first-described unnamed 

 species, the tendrils, in shape like a bird's foot, are of no service 



L J ■- 



