40 AN ANALYSIS OF THE EFFECT OF SELECTION. 
example. These exceptions may still be plausibly ascribed to the inter- 
ference of a multitude of factors, a suggestion not easy to disprove; though it 
seems to me equally likely that segregation has been in reality imperfect.” 
(Bateson, 1914.) 
Fractionation is referred to by Bateson in this same paper as prob- 
ably due to imperfect segregation. Illustrations are Dutch rabbit 
and Picotee and other sweet peas. (See p. 298.) 
“ Accordingly we seem limited to the conclusion that a slowly blending 
gene is involved in the cross between early flowering and late flowering peas, 
that the blending after one generation of heterozygosis may be small in 
amount, but after three generations it is in the majority of cases practically 
complete, so that the commonest ‘constant’ class in the entire hybrid popula- 
tion is one strictly intermediate between the modes of the parental varieties. 
This interpretation is entirely in harmony with the observed modification 
through crossing of many Mendelizing characters, as observed by Daven- 
port, Bateson, and many others in poultry, guinea-pigs, swine, and other 
animals, as well as in plants.”” (Castle, 1916b, p. 215.) 
Hayes (1917) states on the basis of his experiments with variegated 
maize: 
. . One might conclude that certain heterozygous combinations 
produce germinal instability which exhibits itself either as imperfect segrega- 
tion, gametic contamination, or sporophytic variation.” 
In these quotations the following cases have been cited as evidence 
in favor of contamination, and therefore calling for investigation :! 
1. Polydactyl guinea-pigs (Castle, 1906). 6. Merino sheep. 
2. Long-haired guinea-pigs (Castle and | 7. Fantail pigeons. 
Forbes, 1906). 8. Dutch rabbits. 
3. Spotted guinea-pigs and rats (MacCurdy | 9. Picotee and other types of sweet peas. 
and Castle, 1907). 10. Flowering time in peas (Hoshino, 1915). 
4. English rabbits (Castleand Hadley, 1915). | 11. Unspecified case in swine. 
5. Poultry, plumage and toe characters |12. Variegated pericarp in maize (Hayes, 
(Bateson and Davenport). 1917). 
Before we can discuss some of these cases intelligently it is neces- 
sary that we make sure what Castle means by the terms “‘gametic 
purity” and “‘unit-character.” Unless these terms are understood 
in such a way as to eliminate from consideration the idea of recombina- 
tion of independent factors there is, of course, nothing to discuss. 
If by gametic impurity or inconstancy of unit-characters is meant that 
recombination of modifying factors occurs, the existence of such phe- 
nomena must be granted at once—this is, in fact, the main contention 
of the school of ‘‘pure line” advocates or ‘‘mutationists.”’ I think the 
two following quotations from Castle are sufficient to show that there 
need be no disagreement on the question of defining these terms: 
““What we want to get at, if possible, is the objective difference between one 
germ-cell and another, as evidenced by its effect upon the zygote, and it is 
1The rough-coated guinea-pig was formerly cited (e. g., Castle and Phillips, 1914), but is now 
never used. This is because Wright (Castle and Wright, 1916) has shown the results to be due 
to multiple factors. 
