CLIMBING PLANTS. 
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plant P There can be little doubt on this latter point. I think 
we may certainly say that the earliest form which existed 
was a twining plant. We see that twining plants do not 
possess the essential feature of leaf or tendril-bearers, namely, 
the sensitiveness to a touch, which enables a leaf or tendril 
to grasp a stick. But, on the other hand, most leaf and tendril 
climbers do possess the essential quality of a twiner — the 
power of revolving or swinging round, which exists in the 
shoots, leaves, or tendrils of so many of them. This power 
of revolving merely serves in some leaf and tendril climbers 
to carry on the search for supports ; but other leaf and tendril 
climbers, as we have seen, do actually wind spirally round a 
stick exactly like a true twiner. How twiners originally 
obtained their power of swinging round we need not now 
inquire ; it seems to be merely an increase of a similar move- 
ment which is found to occur in a meaningless manner in 
other plants. Thus several flower-stems have been observed 
bowing themselves over and swinging round in small circles, 
like climbing plants. Here the movement is merely an un- 
intelligible concomitant of growth, for, as we see, the move- 
ment is of no advantage to the flower-stem. But the existence 
of this movement is of great interest to us, for it shows how 
a twining plant might be developed by a similar movement 
being found to be advantageous, and being increased by natural 
selection to the requisite extent. 
Another question which may occur to us is this : in what 
way is climbing by leaves or tendrils a more perfect method 
than twining? Why, when a plant had become a twining 
plant, did it not rest satisfied ? The fact that leaf and tendril- 
climbers have been developed out of twiners, and not vice versa , 
is a proof that climbing by leaves or tendrils is a more advan- 
tageous habit than twining ; but we do not see why it should be 
so. If we inquire why any plant has become a climber, we 
shall see the reason. Light is a necessity for all green plants ; 
and a plant which can climb is enabled to escape from the 
shadow of other plants with a far less waste of material than a 
forest-tree, which only pushes its branches into the light by 
sheer growth. Thus the weak, straggling stem of a climbing 
plant gets all the advantages gained by the solid, column-like 
tree trunk. If we apply this test, — which is the most economical 
plan of climbing, twining or leaf-climbing, — we see at once 
that a plant which climbs by seizing wastes far less material 
than one which twines. Thus a kidney-bean which had climbed 
up a stick to a height of two feet, when unwound from its 
support was found to be three feet in length, whereas a pea 
which had climbed up two feet by its tendrils was hardly 
longer than the height reached. Thus the bean had wasted 
