He who will
carefully examine the flowers of orchids for himself will not deny the
existence of the above series of gradations--from a mass of pollen-grains
merely tied together by threads, with the stigma differing but little from
that of the ordinary flowers, to a highly complex pollinium, admirably
adapted for transportal by insects; nor will he deny that all the
gradations in the several species are admirably adapted in relation to the
general structure of each flower for its fertilisation by different
insects. In this, and in almost every other case, the enquiry may be
pushed further backwards; and it may be asked how did the stigma of an
ordinary flower become viscid, but as we do not know the full history of
any one group of beings, it is as useless to ask, as it is hopeless to
attempt answering, such questions.
We will now turn to climbing plants. These can be arranged in a long
series, from those which simply twine round a support, to those which I
have called leaf-climbers, and to those provided with tendrils. In these
two latter classes the stems have generally, but not always, lost the power
of twining, though they retain the power of revolving, which the tendrils
likewise possess. The gradations from leaf-climbers to tendril bearers are
wonderfully close, and certain plants may be differently placed in either
class. But in ascending the series from simple twiners to leaf-climbers,
an important quality is added, namely sensitiveness to a touch, by which
means the foot-stalks of the leaves or flowers, or these modified and
converted into tendrils, are excited to bend round and clasp the touching
object.
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