Hence it probably is,
as Lecoq has remarked, that annual plants are rarely dioecious.
Finally, we have seen reason to believe that the higher plants are
descended from extremely low forms which conjugated, and that the
conjugating individuals differed somewhat from one another,--the one
representing the male and the other the female--so that plants were
aboriginally dioecious. At a very early period such lowly organised
dioecious plants probably gave rise by budding to monoecious plants with
the two sexes borne by the same individual; and by a still closer union
of the sexes to hermaphrodite plants, which are now much the commonest
form. (10/63. There is a considerable amount of evidence that all the
higher animals are the descendants of hermaphrodites; and it is a
curious problem whether such hermaphroditism may not have been the
result of the conjugation of two slightly different individuals, which
represented the two incipient sexes. On this view, the higher animals
may now owe their bilateral structure, with all their organs double at
an early embryonic period, to the fusion or conjugation of two
primordial individuals.) As soon as plants became affixed to the ground,
their pollen must have been carried by some means from flower to flower,
at first almost certainly by the wind, then by pollen-devouring, and
afterwards by nectar-seeking insects. During subsequent ages some few
entomophilous plants have been again rendered anemophilous, and some
hermaphrodite plants have had their sexes again separated; and we can
vaguely see the advantages of such recurrent changes under certain
conditions.
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