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POPULAR SCIENCE REVIEW. 
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 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 Cobsea 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 tendrils, on the other hand, have no 
Fig. 4. 
A caught tendril of Bryonia dioica , spirally contracted in reversed directions. 
hook at the end, and here the tendrils 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, con- 
cluded it was not sensitive. But the fact was that the tendril 
being touched on two sides at once, did not know which 
stimulus to obey, and therefore remained motionless. It was 
in reality extremely sensitive to a touch on any one of its sides. 
There is a remarkable movement which occurs in tendrils 
after they have caught an object, and which renders a tendril a 
better climbing organ than any sensitive leaf. This move- 
ment is called the ‘ spiral contraction/ and is shown in Fig. 4, 
which represents the spirally contracted tendril of the wild 
Bryony ; it may also be seen in Fig. 5, which represents the 
tendril of the Virginian Creeper. When a tendril first seizes 
an object it is quite straight, with the exception of the extreme 
tip, which is firmly curled round the object seized. But in a 
