CLIMBING PLANTS. 



645 



The flexibility of the tendrils is of service in allowing them to be blown 

 about by a breath of wind, and they can thus be made to seize hold of 

 objects which are out of reach of the ordinary revolving movements. 

 Many tendrils can only seize a stick by curling round it, and this even 

 in the most sensitive tendril must take a minute or two ; but with 

 Cobcea the sharp hooks catch hold of little irregularities on the bark 

 the moment the tendril comes into contact with it, and afterward the 

 tendril can curl round and make the attachment permanent. The im- 

 portance of this power of temj)orary attachment is shown by placing 

 a glass rod near a cobsea-plant. Under these conditions the tendrils 

 always fail to get hold of the glass, on which its grapple-like hooks 

 can not seize. 



The movement of the little hook-bearing branches is very remark- 

 able in this species. If a tendril catches an object with one or two 

 hooks, it is not contented, but tries to attach the rest of them in the 

 same way. Now, many of the branches will chance to be so placed that 

 their hooks do not naturally catch, either because they come laterally, 

 or with their blunt backs against the wood, but after a short time, by 

 a process of twisting and adjusting, each little hook becomes turned, 

 so that its sharp point can get a hold on the wood. 



The sharp hook on the tendrils of Cobcea is only a very perfect form 

 of the bluntly curved tip which many tendrils possess, and which 

 serves the same purpose of temporarily holding the object caught until 

 the tendril can curl over and make it secure. There is a curious proof 

 of the usefulness of even this blunt hook in the fact that the tendril is 

 only sensitive to a touch on the inside of the hook. The tendril, when 

 it comes against a twig, always slips up it till the hook catches on it, 

 so that it would be of no use to be sensitive on the convex side. Some 



Fig. 4. A caught tendril of Bryonia dioica, spirally contracted in reversed directions. 



tendrils, on the other hand, have no hook at the end, and here the ten- 

 drils are sensitive to a touch on any side. These tendrils led my 

 father at first into a curious mistake, which he mentions in his book. 

 He pinched a tendril gently in his fingers, and, finding that it did not 

 move, concluded it was not sensitive. But the fact was that the ten- 

 dril, being touched on two sides at once, did not know which stimulus 



