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OBSERVATIONS FOR YOUNG BOTANISTS. 
VII. — Special Modifications and Adaptations of Leaves. 
E have already considered the duties of an ordinary or 
typical leaf; but since Nature is never at a loss for 
resources where some special work is required to be 
done, she frequently diverts the functions of leaves 
into other channels, to suit new habits or to fit the plant better 
to special surroundings. A brief allusion has already been made 
to such cases — as of fleshy leaves in deserts, constructed to store 
water — but it will be as well to devote an article to this subject. 
Climbing Plants. — Mention has been made of the Clematis, 
of which we have one native species, C. Vitalba, the traveller’s 
joy. It has a compound leaf of flve leaflets which are jointed, so 
are readily disarticulated in autumn and fall off ; but the petioles 
are required for supporting the plant. This they do by being 
very sensitive to touch, so that when they press against twigs 
in a hedge they soon coil round it. Now a certain amount of 
weight is, so to say, “felt” by the leaf-stalk, as it helps to support 
the plant. And just as a muscle of the arm increases in size 
if weights are frequently lifted, so does this leaf-stalk. If a 
cross section be examined before and some weeks after a leaf has 
caught hold of a twig, the fibro-vascular cords will be found 
increased in size. As a consequence of utilising the leaf-stalks 
for climbing, the blades in some other plants become more or 
less arrested, or even lost altogether. Thus in the garden pea, 
a portion of the leaflets are gone, and in their places are fine 
thread-like tendrils highly sensitive to touch. They represent 
the mid-ribs of the little blades. Now comes into play the 
principle of “compensation;” for to make up for the loss of 
the blades, the stipules are very much enlarged. In one of our 
wild peas, Lathyrus Aphaca, they undertake all the leaf-functions, 
as the leaf is altogether in the form of a tendril. 
In the wild bryony {Bryonia dioica) the long tendril is of the 
nature of a stipule. At first it projects out stiffly, and is in 
constant but slow motion so as to catch hold of something. As 
soon as the hooked tip has secured a hold it grips the object 
tightly ; and then the tendril coils itself up into a number of 
corkscrew-like turns. An interesting thing must now be ob- 
served, viz., that some of the coils run to the right, others to 
the left, and the number is always about the same either way. 
The meaning of this is that by twisting the tendril it becomes 
stronger, but is strained, and unless it is, so to say, untwisted 
by reversing the coils, it might break. Tie a piece of string to 
some object, and when stretched to its full length twist it for 
some time one way. Then slightly relax the string and it 
twists upon itself to relieve the strain to whicli you have sub- 
jected it. Or take a long piece of ribbon, and you will find 
that to “do it up” neatly you must twist it like a figure of 
