As in many widely separated families of plants, single species and
single genera possess the power of revolving, and have thus become twiners,
they must have independently acquired it, and cannot have inherited it from
a common progenitor. Hence, I was led to predict that some slight tendency
to a movement of this kind would be found to be far from uncommon with
plants which did not climb; and that this had afforded the basis for
natural selection to work on and improve. When I made this prediction, I
knew of only one imperfect case, namely, of the young flower-peduncles of a
Maurandia which revolved slightly and irregularly, like the stems of
twining plants, but without making any use of this habit. Soon afterwards
Fritz Muller discovered that the young stems of an Alisma and of a Linum--
plants which do not climb and are widely separated in the natural system--
revolved plainly, though irregularly, and he states that he has reason to
suspect that this occurs with some other plants. These slight movements
appear to be of no service to the plants in question; anyhow, they are not
of the least use in the way of climbing, which is the point that concerns
us. Nevertheless we can see that if the stems of these plants had been
flexible, and if under the conditions to which they are exposed it had
profited them to ascend to a height, then the habit of slightly and
irregularly revolving might have been increased and utilised through
natural selection, until they had become converted into well-developed
twining species.
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