The corresponding experiment could be made with plants of a pure
sugar-race by pollination with hybrid pollen. The spikes would show
exactly the same mixture as in the above case, but now this may be
considered as conclusive proof that half the pollen-grains represent the
quality of one parent and the other half the quality of the other.
Another corollary of Mendel's law is the following. In each generation
two groups return to purity, and one-half remains hybrid. These last
will repeat the same phenomenon of splitting in their progeny, and it is
easily seen that the same rule will hold good for all succeeding
generations. According to Mendel's principle, in each year there is a
new hybridization, differing in no respect from the first and original
one. If the hybrids only are propagated, each year will show one-fourth
of the offspring returning to the specific character, one-fourth
assuming the type of the variety and one-half remaining hybrid. I have
tested this with a hybrid between the ordinary nightshade with black
berries, and its variety, _Solanum nigrum chlorocarpum_, with pale
yellow fruits. Eight generations of the hybrids were cultivated, [299]
disregarding always the reverting offspring. At the end I counted the
progeny of the sixth and seventh generations and found figures for their
three groups of descendants, which exactly correspond to Mendel's
formula.
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