Other plants need cross-fertilization in order to produce a
normal yield of seeds. Here two individuals have always to be combined,
and the pedigree becomes a more complicated one. Such is the case with
the toad-flax, which is nearly sterile with its own pollen. But even in
these cases the visits of insects bringing pollen [26] from other
plants, must be carefully excluded. A special lecture will be devoted to
this very interesting source of impurity and of uncertainty in ordinary
cultures.
Of course, crosses may lie in the proposed line of work, and this is the
third point to be alluded to. They must be surrounded with the same
careful isolation and protection against bees, as any other
fertilizations. And not only the seed-parent, but also the pollen must
be kept pure from all possible foreign admixtures.
A pure and accurately recorded ancestry is thus to be considered as the
most important condition of success in experimental plant breeding. Next
to this comes the gathering of the seeds of each individual separately.
Fifty or sixty, and often more, bags of seeds are by no means uncommon
for a single experiment, and in ordinary years the harvest of my garden
is preserved in over a thousand separate lots.
Complying with these conditions, the origin of species may be seen as
easily as any other phenomenon.
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