flowers can be interbred more closely than is possible with bisexual
animals, and are therefore well-fitted to throw light on the nature and
extent of the good effects of crossing, and on the evil effects of close
interbreeding or self-fertilisation. The most important conclusion at
which I have arrived is that the mere act of crossing by itself does no
good. The good depends on the individuals which are crossed differing
slightly in constitution, owing to their progenitors having been
subjected during several generations to slightly different conditions,
or to what we call in our ignorance spontaneous variation. This
conclusion, as we shall hereafter see, is closely connected with various
important physiological problems, such as the benefit derived from
slight changes in the conditions of life, and this stands in the closest
connection with life itself. It throws light on the origin of the two
sexes and on their separation or union in the same individual, and
lastly on the whole subject of hybridism, which is one of the greatest
obstacles to the general acceptance and progress of the great principle
of evolution.

In order to avoid misapprehension, I beg leave to repeat that throughout
this volume a crossed plant, seedling, or seed, means one of crossed
PARENTAGE, that is, one derived from a flower fertilised with pollen
from a distinct plant of the same species. And that a self-fertilised
plant, seedling, or seed, means one of self-fertilised PARENTAGE, that
is, one derived from a flower fertilised with pollen from the same
flower, or sometimes, when thus stated, from another flower on the same
plant.



CHAPTER II.