e original hybrids, splitting up in the next generation
in the same arithmetical proportion as before.

Accordingly, if we confine our study to the two contrasted characters,
tallness and dwarfness, we see that just three kinds of peas exist,
namely, dwarfs which breed true, talls which breed true, and talls which
always give the same definite proportion of talls and dwarfs among their
descendants. Innumerable experiments which have since been made with
other pairs of characters have demonstrated that this same mathematical
proportion holds good throughout the whole world of plants and
animals;[25] and hence this astonishing result is now called Mendel's
Law, and is regarded as the most important discovery in biology in
several generations.

[Footnote 25: When dealing with only a few individual cases, we do not
always find them to come out in such exact proportion; but when the
number of examples is large, the proportion is so close to these figures
that the exceptions can be entirely neglected as probably due to error
of some kind.]

There are two distinct kinds of Andalusian fowls, one pure bred black,
the other pure bred white with slight dashes of black here and there.
When these are mated, no matter which color is the father or the mother,
the next or hybrid generation are always a queer mixture of black and
white called by fanciers blue. When these blues are interbred,
one-quarter of their offspring will be white, which will prove to breed
true ever afterwards, one-quarter will be black that will breed true,
and fifty per cent. will be blue which will break up in the next
generation in the very same way as before. In this case neither white
nor black character is dominant, and accordingly we have a blending of
both in the first hybrid generation.

In guinea pigs, black color has been found to be dominant over white,
rough coat over smooth coat, and short hair over long hair. These
remarkable results following from an experimental trial of Mendelism
have stimulated hosts of investigators in all parts of the world, until
now many varieties of plants and animals have been studied for many
successive generations, already, building up a considerable literature
dealing with the subject.

Perhaps the most extensive and exact series of experiments along this
line have been carried on by Thomas Hunt Morgan and his assistants, of
Columbia University. For over five years they have been breeding the
wild fruit fly (_Dro