innaeus has remarked on the sterility of nearly all
alpine flowers when cultivated in a lowland district{252}. Perhaps the
immense class of double flowers chiefly owe their structure to an excess
of food acting on parts rendered slightly sterile and less capable of
performing their true function, and therefore liable to be rendered
monstrous, which monstrosity, like any other disease, is inherited and
rendered common. So far from domestication being in itself unfavourable
to fertility, it is well known that when an organism is once capable of
submission to such conditions <its> fertility is increased{253} beyond the
natural limit. According to agriculturists, slight changes of
conditions, that is of food or habitation, and likewise crosses with
races slightly different, increase the vigour and probably the fertility
of their offspring. It would appear also that even a great change of
condition, for instance, transportal from temperate countries to India,
in many cases does not in the least affect fertility, although it does
health and length of life and the period of maturity. When sterility is
induced by domestication it is of the same kind, and varies in degree,
exactly as with hybrids: for be it remembered that the most sterile
hybrid is no way monstrous; its organs are perfect, but they do not act,
and minute microscopical investigations show that they are in the same
state as those of pure species in the intervals of the breeding season.
The defective pollen in the cases above alluded to precisely resembles
that of hybrids. The occasional breeding of hybrids, as of the common
mule, may be aptly compared to the most rare but occasional reproduction
of elephants in captivity. The cause of many exotic Geraniums producing
(although in vigorous health) imperfect pollen seems to be connected
with the period when water is given them{254}; but in the far greater
majority of cases we cannot form any conjecture on what exact cause the
sterility of organisms taken from their natural conditions depends. Why,
for instance, the cheetah will not breed whilst the common cat and
ferret (the latter generally kept shut up in a small box) do,--why the
elephant will not whilst the pig will abundantly--why the partridge and
grouse in their own country will not, whilst several species of
pheasants, the guinea-fowl from the deserts of Africa and the peacock
from the jungles of India, will. We must, however, feel convinced that
it depends on