this doctrine of heredity is known as Mendelism; it is the principle of
inheritance through the pure transmission of unit characters.

An illustration will probably make the Mendelian principle clear. Let us
select our illustration from the plant world. It is found that if white
and yellow corn are crossed, all the corn the first year, resulting from
this crossing, will be yellow. Now, if this hybrid yellow corn is
planted the second year, and freely cross-fertilized, it turns out that
one fourth of it will be white and three fourths yellow. But this yellow
consists of three parts: one part being pure yellow which will breed
true, producing nothing but yellow; the other two parts transmit white
and yellow in equal ratio. That is to say, these two parts are hybrids,
the result of crossing white with yellow. It is not meant that one can
actually distinguish these two kinds of yellow, the pure yellow and the
hybrid yellow, but the results from planting it show that one third of
the yellow is pure and that the other two thirds transmit white and
yellow in equal ratio.

The main point to notice in all this is that when two individuals having
diverse characteristics are crossed, the characteristics do not fuse and
disappear ultimately, but that the two characteristics are transmitted
in equal ratio, and each will appear in succeeding generations, and will
appear pure, just as if it had not been crossed with something
different. The first offspring resulting from the cross--known as
hybrids--may show either one or the other of the diverse
characteristics, or, when such a thing is possible, even a blending of
the two characteristics. But whatever the actual appearance of the first
generation of offspring resulting from crossing parents having diverse
characteristics, their germ-cells transmit the diverse characteristics
in equal proportion, as explained above.