, as we have seen, diminishes the evil from close
interbreeding,--will occasionally be introduced into each district.

Experiments have not been tried on the effects of fertilising flowers
with their own pollen during _several_ generations. But we shall
presently see that certain plants, either normally or abnormally, are
more or less sterile, even in the first generation, when fertilised by
their own pollen. Although nothing is directly known on the evil
effects of long-continued close interbreeding with plants, the converse
proposition that great good is derived from crossing is well
established.

With respect to the crossing of individuals belonging to the same
sub-variety, Gaertner, whose accuracy and experience exceeded that of
all other hybridisers, states[284] that he has many times observed good
effects from this step, especially with exotic genera, of which the
fertility is somewhat impaired, such as Passiflora, Lobelia, and
Fuchsia. Herbert also says,[285] "I am inclined to think that I have
derived advantage from impregnating the flower from which I wished to
obtain seed with pollen from another individual of the same variety, or
at least from another flower, rather than with its own." Again,
Professor Lecoq asserts that he has ascertained that crossed offspring
are more vigorous and robust than their parents.[286]

General statements of this kind, however, can seldom be fully trusted;
consequently I have begun a series of experiments, which, if they
continue to give the same results as hitherto, will for ever settle the
question of the good effects of crossing two distinct plants of the
same variety, and of the evil effects of self-fertilisation. A clear
light will thus also be thrown on the fact that flowers are invariably
constructed so as to permit, or favour, or necessitate the union of two
individuals. We shall clearly understand why monoecious and
dioecious,--why dimorphic and trimorphic plants exist, and many other
such cases. The plan which I have followed in my experiments is to grow
plants in the same pot, or in pots of the same size, or close together
in the open ground; to carefully exclude insects; and then to fertilise
some of the flowers with pollen from the same flower, and others on the
same plant with pollen from a distinct but adjoining plant. In many,