On this principle Marshall formerly remarked, with respect to the sheep of part of Yorkshire, "As they generally belong to poor people, and are mostly IN SMALL LOTS, they never can be improved.

" On the other hand, nurserymen, from keeping large stocks of the same plant, are generally far more successful than amateurs in raising new and valuable varieties.

A large number of individuals of an animal or plant can be reared only where the conditions for its propagation are favourable.

When the individuals are scanty all will be allowed to breed, whatever their quality may be, and this will effectually prevent selection.