th dwarf pea. Gametes
represented by small and zygotes by larger circles.]

We may now proceed with the help of the accompanying scheme (Fig. 1) to
deduce the results that should flow from Mendel's conception of the nature
of the gametes, and to see how far they are in accordance with the facts.
Since the original tall plant belonged to a strain which bred true, all the
gametes produced by it must bear the tall character. Similarly all the
gametes of the original dwarf plant must bear the dwarf character. A cross
between these two means the union of {22} a gamete containing tallness with
one bearing dwarfness. Owing to the completely dominant nature of the tall
character, such a plant is in appearance indistinguishable from the pure
tall, but it differs markedly from it in the nature of the gametes to which
it gives rise. When the formation of the gametes occurs, the elements
representing dwarfness and tallness SEGREGATE from one another, so that
half of the gametes produced contain the one, and half contain the other of
these two elements. For on hypothesis every gamete must be pure for one or
other of these two characters. And this is true for the ovules as well as
for the pollen grains. Such hybrid F_1 plants, therefore, must produce a
series of ovules consisting of those bearing tallness and those bearing
dwarfness, and must produce them in equal numbers. And similarly for the
pollen grains. We may now calculate what should happen when such a series
of pollen grains meets such a series of ovules, _i.e._ the nature of the
generation that should be produced when the hybrid is allowed to fertilise
itself. Let us suppose that there are 4x ovules so that 2x are "tall" and
2x are "dwarf." These are brought in contact with a mass of pollen grains
of which half are "tall" and half are "dwarf." It is obvious that a "tall"
ovule has an equal chance of being fertilised by a "tall" or a "dwarf"
pollen grain. Hence of our 2x "tall" ovules, x will be fertilised by "tall"
pollen grains and x will be fertilised by "dwarf" pollen grains. The former
must give rise to tall {23} plants, and since the dwarf character has been
entirely eliminated from them they must in the future breed true. The
latter must also give rise to tall plants, but since they carry also the
recessive dwarf character they must when bred from produce both tails and
dwarfs. Each of the 2x dwarf ovules, again, has an equal chance of being
fertilised by a "tall" or by