If species become modified in the course of ages, as almost
all naturalists now admit, we may conclude that L. nissolia has
passed through a series of changes, in some degree like those here
indicated.
The most interesting point in the natural history of climbing plants
is the various kinds of movement which they display in manifest
relation to their wants. The most different organs--stems, branches,
flower-peduncles, petioles, mid-ribs of the leaf and leaflets, and
apparently aerial roots--all possess this power.
The first action of a tendril is to place itself in a proper
position. For instance, the tendril of Cobaea first rises vertically
up, with its branches divergent and with the terminal hooks turned
outwards; the young shoot at the extremity of the stem is at the same
time bent to one side, so as to be out of the way. The young leaves
of Clematis, on the other hand, prepare for action by temporarily
curving themselves downwards, so as to serve as grapnels.
Secondly, if a twining plant or a tendril gets by any accident into
an inclined position, it soon bends upwards, though secluded from the
light. The guiding stimulus no doubt is the attraction of gravity,
as Andrew Knight showed to be the case with germinating plants.
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