Theory of Plant Breeding 
will be seen, three to one. The explanation as given 
by Mendel was very simple and effective. 
We will suppose that, when “yellow” and “green” 
elements occur together in one germ cell, the progeny 
must be yellow, that is, we will suppose that yellow 
dominates over green, or is a dominant, whilst yellow is 
recessive, using the original terms, 
Then if we suppose that the first generation is all 
mixed, we may represent them as (G+Y),(G+Y). If 
those first generation hybrids are crossed we may take 
their constitution as follows: GG, GY, YG, YY. 
The GG are pure green, and the YY are pure yellow, 
but both GY and YG will appear yellow because the 
yellow dominates the green, so that the proportion of 
three yellow to one green is maintained because yellow 
dominates over green. 
Both GG and YY are pure green and yellow respec- 
tively, and should breed true for any number of genera- 
tions so far as this one character is concerned and if not 
influenced by change in the environments. 
It is clear that this theory explains many cases of 
heredity “ skipping a generation,” and of reversion to an 
earlier type. So the theory is of very great importance 
to all hybridisers and those seeking to fix a new and 
valuable character. As Mr. Bateson, the great authority 
on this question, has said, it may enable a practical 
breeder to fix his type in four instead of in ten or 
twelve generations. 
Mendel’s theory has been tested in a very large 
number of cases. It has been found to apply to certain 
characters of peas, of poultry (colour and comb), of 
horses (colour), of rabbits (colour), of mice (“ waltzing ” 
and colour), and especially it was found to holdin no less 
than 4548 pairs of specific characters in orchid hybrids. 
In this last experiment conducted by Hurst,” the re- 
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