The stem twines indifferently to the right
or left. Some others species of Solanum, and of another genus, viz.
Habrothamnus, belonging to the same family, are described in
horticultural works as twining plants, but they seem to possess this
faculty in a very feeble degree. We may suspect that the species of
these two genera have as yet only partially acquired the habit of
twining. On the other hand with Tecoma radicans, a member of a
family abounding with twiners and tendril-bearers, but which climbs,
like the ivy, by the aid of rootlets, we may suspect that a former
habit of twining has been lost, for the stem exhibited slight
irregular movements which could hardly be accounted for by changes in
the action of the light. There is no difficulty in understanding how
a spirally twining plant could graduate into a simple root-climber;
for the young internodes of Bignonia Tweedyana and of Hoya carnosa
revolve and twine, but likewise emit rootlets which adhere to any
fitting surface, so that the loss of twining would be no great
disadvantage and in some respects an advantage to these species, as
they would then ascend their supports in a more direct line.
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