e of crossing with a fresh stock
rests on the same ground--a union of sexual cells possessing somewhat
different characters--as the fact that many hybrids are distinguished
by greater luxuriance, wealth of flowers, etc. corresponds entirely
with Darwin's conclusions. It seems to me to follow clearly from
his investigations that there is no essential difference between
cross-fertilisation and hybridisation. The heterostyled plants are
normally dependent on a process corresponding to hybridisation. The view
that specifically distinct species could at best produce sterile hybrids
was always opposed by Darwin. But if the good results of crossing were
EXCLUSIVELY dependent on the fact that we are concerned with hybrids,
there must then be a demonstration of two distinct things. First, that
crossing with a fresh stock belonging to the same systematic entity
or to the same hybrid, but cultivated for a considerable time under
different conditions, shows no superiority over self-fertilisation,
and that in pure species crossing gives no better results than
self-pollination. If this were the case, we should be better able to
understand why in one plant crossing is advantageous while in others,
such as Darwin's Hero and the forms of Mimulus and Nicotiana no
advantage is gained; these would then be pure species. But such a
proof has not been supplied; the inference drawn from cleistogamous and
cleistopetalous plants is not supported by evidence, and the experiments
on geitonogamy and on the advantage of cross-fertilisation in species
which are usually self-fertilised are opposed to this view. There are
still but few researches on this point; Darwin found that in Ononis
minutissima, which produces cleistogamous as well as self-fertile
chasmogamous flowers, the crossed and self-fertilised capsules
produced seed in the proportion of 100:65 and that the average bore the
proportion 100:86. Facts previously mentioned are also applicable to
this case. Further, it is certain that the self-sterility exhibited by
many plants has nothing to do with hybridisation. Between self-sterility
and reduced fertility as the result of self-fertilisation there is
probably no fundamental difference.

It is certain that so difficult a problem as that of the significance
of sexual reproduction requires much more investigation. Darwin was
anything but dogmatic and always ready to alter an opinion when it was
not based on definite proof: he wrote, "But the vei