COMPOUND ALLELOMORPHS 161 



cerebral hernia, crest, muff, tail length, vulture hock, foot- feathering, 

 foot-colour, earlobe, and both general and special plumage colour. 

 Everywhere unit characters are changed by hybridizing." 1 Clearly, 

 then, as is sometimes the case with the sexual characters, especially 

 the less stringently selected secondary sexual characters (e.g. in 

 human ' hermaphrodites '), the allelomorph, which is supposed by 

 Mendelians to be absent, very often, indeed almost always makes 

 its presence felt. We must assume, therefore, that before separat- 

 ing if they do separate the alternative units if there are any 

 units infect one another (z.^blend) so as to form hybrid units ; or 

 else we must assume that they do not blend, but remain together, 

 and that one (but not always the same one) dominates more or 

 less completely over the other. In any case, " construed in the 

 strictestsense the doctrine of gametic purity is untenable." 2 



275. Now ample evidence exists that allelomorphs sometimes 

 combine to form compound allelomorphs. When two varieties 

 are crossed, one or other form may dominate, or the type may 

 blend, or the ancestral type may appear. When this, the first 

 mongrel generation, is self-fertilized or bred together, it sometimes 

 happens that there is no return in the offspring to the grandparents 

 (the types that were crossed). On the contrary the descendants 

 break up into two or more forms distinct from the grandparents, 

 one or more of which may breed true. For example, if the Stanley 

 sweet-pea, which has dark maroon petals (standards and wings), 

 be crossed with the Giant White, the offspring are Giant Purple 

 Invincibles with maroon standards and blue wings. " These first- 

 crosses, self-fertilized, gave Giant White, Giant Purple (without 

 blue wings), Mars (a well-known red variety), Her Majesty (a full 

 magenta, well-known), and a form like Her Majesty, but flaked 

 with white. One plant of each was saved and its self-fertilized seed 

 sown. Mars and Her Majesty came true. The Giant White was 

 tested, and it came true also. The Her Majesty flaked with white, 

 however, gave Whites, Her Majesty, and Her Majesty flaked white 

 again. The Giant Purple gave Giant White, Her Majesty, Giant 

 Purples, and two plants of a streaky cream colour. . . . We are 

 then led to the conclusion that the allelomorph transmitting the 

 coloration of Stanley is compound, and that it can be broken up 

 into simpler and possibly component elements." 3 



1 Inheritance in Poultry, p. 80. 



2 Castle and Allen, The Heredity of Albinism. Proceedings of the American 

 Academy of Arts and Sciences, vol. xxxviii. No. 21, p. 615. 



3 First Report to Evolution Committee, pp. 142-3. See also Bateson, Mendel's 

 Principles of Heredity ,fpp. 60 et seq. 



II 



