If a
shoot of any ordinary plant be placed in an inclined position in a
glass of water in the dark, the extremity will, in a few hours, bend
upwards; and if the position of the shoot be then reversed, the
downward-bent shoot reverses its curvature; but if the stolen of a
strawberry, which has no tendency to grow upwards, be thus treated,
it will curve downwards in the direction of, instead of in opposition
to, the force of gravity. As with the strawberry, so it is generally
with the twining shoots of the Hibbertia dentata, which climbs
laterally from bush to bush; for these shoots, if placed in a
position inclined downwards, show little and sometimes no tendency to
curve upwards.
Thirdly, climbing plants, like other plants, bend towards the light
by a movement closely analogous to the incurvation which causes them
to revolve, so that their revolving movement is often accelerated or
retarded in travelling to or from the light. On the other hand, in a
few instances tendrils bend towards the dark.
Fourthly, we have the spontaneous revolving movement which is
independent of any outward stimulus, but is contingent on the youth
of the part, and on vigorous health; and this again of course depends
on a proper temperature and other favourable conditions of life.
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