Tendrils
soon after catching a support grow much stronger and thicker, and
sometimes more durable to a wonderful degree; and this shows how much
their internal tissues must be changed. Occasionally it is the part
which is wound round a support which chiefly becomes thicker and
stronger; I have seen, for instance, this part of a tendril of
Bignonia aequinoctialis twice as thick and rigid as the free basal
part. Tendrils which have caught nothing soon shrink and wither; but
in some species of Bignonia they disarticulate and fall off like
leaves in autumn.
Any one who had not closely observed tendrils of many kinds would
probably infer that their action was uniform. This is the case with
the simpler kinds, which simply curl round an object of moderate
thickness, whatever its nature may be. {36} But the genus Bignonia
shows us what diversity of action there may be between the tendrils
of closely allied species. In all the nine species observed by me,
the young internodes revolve vigorously; the tendrils also revolve,
but in some of the species in a very feeble manner; and lastly the
petioles of nearly all revolve, though with unequal power. The
petioles of three of the species, and the tendrils of all are
sensitive to contact.
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