breeding capacity, the only way
to do this is to save the seed from a number of such plants _individually_,
and to raise a further generation. Some of them will be found to breed
true. The variety is then established, and may at once be put on the market
with full confidence that it will hereafter throw none of the other forms.
The all-important thing is to save and sow the seed of separate individuals
separately. However alike they look, the seed from different individuals
must on no account be mixed. Provided that due care is taken in this
respect no long and tedious process of selection is required for the
fixation of any given variety. Every possible variety arising from a cross
appears in the F_2 generation if only a sufficient {155} number is raised,
and of all these different varieties a certain proportion of each is
already fixed. Heredity is a question of individuals, and the recognition
of this will save the breeder much labour, and enable him to fix his
varieties in the shortest possible time.

Such cases as these of the sweet pea throw a fresh light upon another of
the breeder's conceptions, that of purity of type. Hitherto the criterion
of a "pure-bred" thing, whether plant or animal, has been its pedigree, and
the individual was regarded as more or less pure bred for a given quality
according as it could show a longer or shorter list of ancestors possessing
this quality. To-day we realise that this is not essential. The pure-bred
picotee appears in our F_2 family though its parent was a purple bicolor,
and its remoter ancestors whites for generations. So also from the cross
between pure strains of black and albino rabbits we may obtain in the F_2
generation animals of the wild agouti colour which breed as true to type as
the pure wild rabbit of irreproachable pedigree. The true test of the pure
breeding thing lies not in its ancestry but in the nature of the gametes
which have gone to its making. Whenever two similarly constituted gametes
unite, whatever the nature of the parents from which they arose, the
resulting individual is homozygous in all respects and must consequently
breed true. In deciding questions of purity it is to the gamete, and not to
ancestry, that our appeal must henceforth be made. {156}

Improvement is after all the keynote to the breeder's operations. He is
aiming at the production of a strain which shall combine the greatest
number of desirable properties with the least number of und