nd the relatively large size to
which they attain, many of the properties of zygotes are appreciable by
observation. The colour of an animal or of a flower, the shape of a seed,
or the pattern on the wings of a moth are all zygotic properties, and all
capable of direct estimation. It is otherwise with the properties of
gametes. While the difference between a black and a white fowl is
sufficiently obvious, no one by inspection can tell the difference between
the egg that will hatch into a black and that which will hatch into a
white. Nor from a mass of pollen grains can any one to-day pick out those
that will produce white from those that will produce coloured flowers.
Nevertheless, we know that in spite of apparent similarity there must exist
fundamental differences among the gametes, even {7} among those that spring
from the same individual. At present our only way of appreciating those
differences is to observe the properties of the zygotes which they form.
And as it takes two gametes to form a zygote, we are in the position of
attempting to decide the properties of two unknowns from one known.
Fortunately the problem is not entirely one of simple mathematics. It can
be attacked by the experimental method, and with what measure of success
will appear in the following pages.

* * * * *

{8}

CHAPTER II

HISTORICAL

To Gregor Mendel, monk and abbot, belongs the credit of founding the modern
science of heredity. Through him there was brought into these problems an
entirely new idea, an entirely fresh conception of the nature of living
things. Born in 1822 of Austro-Silesian parentage, he early entered the
monastery of Bruenn, and there in the seclusion of the cloister garden he
carried out with the common pea the series of experiments which has since
become so famous. In 1865 after eight years' work he published the results
of his experiments in the _Proceedings of the Natural History Society of
Bruenn_, in a brief paper of some forty pages. But brief as it is the
importance of the results and the lucidity of the exposition will always
give it high rank among the classics of biological literature. For
thirty-five years Mendel's paper remained unknown, and it was not until
1900 that it was simultaneously discovered by several distinguished
botanists. The causes of this curious neglect are not altogether without
interest. Hybridisation experiments before Mendel there had been in plenty