A. D. Darbishire. 
176 
to adulterate that of the yellow with green; and in this way it was 
possible to make the difference between the expectation based on 
Mendel’s theory and the theory of ancestral contribution very great. 
The green which I used to make the cross with was an 
“extracted” green in F 5 produced from a cross originally made by 
Mr. C. C. Hurst who very kindly gave me a sample of F 3 cotyledons. 
These greens, it will be seen, number no greens amongst their 
ancestors until the original green used by Mr. Hurst to make the 
cross, is reached. That is to say its pedigree, if we pay attention 
solely to individuals in the direct line of ascent and signify yellow by 
Y and green by G, is as given below, writing only one of each letter 
where the two parents are the same. 
The extracted green used in the experiment is denoted by the 
circle at the base of the chain. Those familiar with Mendelian 
theory will see that such a green is, in spite of its ancestry, exactly 
similar in constitution with a green of pure race, that is a green with 
nothing but green ancestry for many generations back; whereas, 
of course, the view based on the theory of ancestral contributions 
is that it is a very different thing from a green of pure race. And 
whilst the Mendelian theory would assert that the F 2 resulting from a 
cross between a yellow and such an “ adulterated ” green would not 
differ from the F 2 from a cross between a yellow and green, both of 
pure race; the theory of ancestral contribution is committed to the 
prediction that the number of greens in the F 2 from the cross between 
the yellow and the green with yellow ancestry, will be considerably 
less than the number of them in the F„ from the cross between the 
yellow and green, both of pure race. The difference between the 
ancestry of the two crosses may be conveniently summarized in the 
two pedigrees A and B. 
