t that mere individual differences are not amply sufficient,
with extreme care, to allow of the accumulation of a large amount
of modification in almost any desired direction. But as variations
manifestly useful or pleasing to man appear only occasionally, the
chance of their appearance will be much increased by a large number
of individuals being kept; and hence this comes to be of the highest
importance to success. On this principle Marshall has remarked, with
respect to the sheep of parts of Yorkshire, that "as they generally
belong to poor people, and are mostly IN SMALL LOTS, they never can be
improved." On the other hand, nurserymen, from raising large stocks
of the same plants, are generally far more successful than amateurs in
getting new and valuable varieties. The keeping of a large number of
individuals of a species in any country requires that the species should
be placed under favourable conditions of life, so as to breed freely in
that country. When the individuals of any species are scanty, all the
individuals, whatever their quality may be, will generally be allowed
to breed, and this will effectually prevent selection. But probably the
most important point of all, is, that the animal or plant should be
so highly useful to man, or so much valued by him, that the closest
attention should be paid to even the slightest deviation in the
qualities or structure of each individual. Unless such attention be paid
nothing can be effected. I have seen it gravely remarked, that it was
most fortunate that the strawberry began to vary just when gardeners
began to attend closely to this plant. No doubt the strawberry had
always varied since it was cultivated, but the slight varieties had been
neglected. As soon, however, as gardeners picked out individual plants
with slightly larger, earlier, or better fruit, and raised seedlings
from them, and again picked out the best seedlings and bred from them,
then, there appeared (aided by some crossing with distinct species)
those many admirable varieties of the strawberry which have been raised
during the last thirty or forty years.

In the case of animals with separate sexes, facility in preventing
crosses is an important element of success in the formation of new
races,--at least, in a country which is already stocked with other
races. In this respect enclosure of the land plays a part. Wandering
savages or the inhabitants of open plains rarely possess more than one
breed of