In the class Monoecia of Linnaeus, Delpino shows that the
species of twenty-eight genera are anemophilous, and of seventeen genera
entomophilous. (10/57. 'Studi sopra un Lignaggio anemofilo delle
Compositae' 1871.) The larger proportion of entomophilous genera in this
latter class is probably the indirect result of insects having the power
of carrying pollen to another and sometimes distant plant much more
securely than the wind. In the above two classes taken together there
are thirty-eight anemophilous and thirty-six entomophilous genera;
whereas in the great mass of hermaphrodite plants the proportion of
anemophilous to entomophilous genera is extremely small. The cause of
this remarkable difference may be attributed to anemophilous plants
having retained in a greater degree than the entomophilous a primordial
condition, in which the sexes were separated and their mutual
fertilisation effected by means of the wind. That the earliest and
lowest members of the vegetable kingdom had their sexes separated, as is
still the case to a large extent, is the opinion of a high authority,
Nageli. (10/58. 'Entstehung und Begriff der Naturhist. Art' 1865 page
22.) It is indeed difficult to avoid this conclusion, if we admit the
view, which seems highly probable, that the conjugation of the Algae and
of some of the simplest animals is the first step towards sexual
reproduction; and if we further bear in mind that a greater and greater
degree of differentiation between the cells which conjugate can be
traced, thus leading apparently to the development of the two sexual
forms.
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