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POPULAR SCIENCE REVIEW. 
Some of the problems, as, for instance, why twining plants 
cannot as a rule climb thick stems, may be looked at from the 
natural-history point of view. Most of our climbing plants 
die down in the winter, so that if they were able to climb round 
big tree trunks, they would waste all the precious summer 
weather in climbing a few feet, whereas the same amount 
of longitudinal growth devoted to twining up a thin stick would 
have raised them up to the light after which they are striving. 
And as a plant exercises no choice, but merely swings round 
till it hits against an object, up which it will then try to 
twine, it seems as if the inability to climb thick stems might 
be a positive advantage to a plant, by forcing it to twine up 
such objects as would best repay the trouble. 
In the classification of climbing plants, proposed by my 
father in his book, he makes a subdivision of ‘ hook- climbers/ 
These may be taken as the simplest representatives of that class 
of climbers which are not twining plants. The common bramble 
climbs or scrambles up through thick underwood, being 
assisted by the re- curved spines which allow the rapidly- 
growing shoot to creep upwards as it lengthens, but prevent 
it from slipping backwards again ; the common goose-grass, 
(Galium) also climbs in this way, sticking like a burr to the 
side of a hedge-row up which it climbs. Most country boys 
will remember having taken advantage of this burr-like 
quality of Galium in making sham birds’ nests, the prickly 
stems adhering together in the desired form. Such plants as 
the bramble or Galium exhibit none* of the swinging round 
movement which I have described in twiners : they simply grow 
straight on, trusting to their hooks to retain the position gained. 
In some species of Clematis we find a mechanism, which 
reminds one of a simple hook climber, but is in reality a much 
better arrangement. The young leaves projecting outwards 
and slightly backwards from the stem, may remind us of the 
hooked spines of a bramble, and like them easily catch on 
neighbouring objects, and support the trailing stem. Or the 
leaf of the species of Clematis given in Fig. 1, may serve as 
an example of a leaf acting like a hook. The main stalk of 
the leaf is seen to be bent angularly downwards at the points 
where each successive pair of leaflets is attached, and the leaflet 
at the end of the leaf is bent down at right angles, and thus 
forms a grappling apparatus. The Clematis does not, like the 
bramble, trust to mere growth, to thrust itself among tangled 
bushes, but possesses the same powers of revolving in search of 
* That is to say, the revolving movement is not sufficiently developed to 
be of practical importance. The same remark is applicable to the other 
cases in which I have spoken of the absence of revolving movement in the 
growing parts of plants. 
