" 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.

But probably the most important element is that the animal or plant should be so highly valued by man, that the closest attention is paid to even the slightest deviations in its qualities or structure.