The closure of the
flowers will also exclude nocturnal insects which may be ill-adapted for
their fertilisation, and the well-adapted kinds at periods when the
temperature is not favourable for fertilisation. Whether these movements of
the petals consist, as is probable, of modified circumnutation we do not
know.
Embryology of Leaves.--A few facts have been incidentally given in this
chapter on what may be called the embryology of leaves. With most plants
the first leaf which is developed after the cotyledons, resembles closely
the leaves produced by the mature plant, but this is not always the case.
the first leaves produced by some species of Drosera, for instance by D.
Capensis, differ widely in shape from those borne by the mature plant, and
resemble closely the leaves of D. rotundifolia, as was shown to us by Prof.
Williamson of Manchester. The first true leaf of
* 'Die Schutzmittel des Pollens,' 1873, pp. 30-39.
[page 415]
the gorse, or Ulex, is not narrow and spinose like the older leaves. On the
other hand, with many Leguminous plants, for instance, Cassia, Acacia
lophantha, etc.
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