CLIMBING PLANTS. 
219 
a support which, simple or true twining plants possess. In- 
deed, many species of Clematis are actually twining plants, and 
can wind spirally up a stick placed in their way. And the 
same revolving movement which enables them thus to wind 
spirally, also helps them to search for some holding place for 
their hook- or grapple-like leaves, and in many species the 
search is carried on by the leaves swinging round, quite in- 
dependently of the revolving movement of the stem on which 
they are borne. 
If a leaf of a Clematis succeed by any means in hooking on 
to a neighbouring object, the special characteristic of leaf- 
climbing plants comes into play. The stalk of the leaf curls 
strongly over towards the object touching it, and clasps it 
firmly. It is obvious how great is the advantage thus gained 
over a mere hook. A leaf such as that shown in Fig. 2 might 
Fig. 1 * 
A young leaf of Clematis viticella. 
Fig. 2. Clematis glandulosa. 
With two young leaves clasping two 
twigs, with the clasping portions 
thickened. 
be made to catch on to a neighbouring twig by its bent stalk, 
in such a way, that although it managed to stay where it was, it 
could bear none of the weight of the plant, and would be liable 
to be displaced by a strong wind or other disturbance. But 
when the stalk of the leaf had curled close round the twig, 
nothing could displace it, and it could take its share in the work 
of supporting the plant. 
The extreme sensitiveness of the leaf- stalk to slight and 
gentle touches, gives a curious idea of the alertness of the plant 
in its search for supporting objects. A leaf may be excited to 
bend, by a loop of string weighing only T V grain. It is an 
* For the loan of this and the other woodcuts illustrating this article, 
we are indebted to the kindness of Mr. Charles Darwin and Mr. Murray. 
