COLOUR INHERITAKCE IX PIGEOXS. 607 



It should perhaps be noted that although tlie individual matings 

 show, considering the small numbers, a very close a^jproximatiou 

 to the expected results, yet at the same time the tendency to vary 

 from the anticipated results is all in one direction, viz. to a greater 

 number of Chequered birds. This is most marked in those 

 matings where equality was expected, for of the 28 birds bred, 

 19 were Chequers; in those cases where the- expectation was 3:1, 

 21 birds were bred of which 15 were Chequers, which is approxi- 

 mately correct. It is possibly due as much to this tendency as 

 to the unconscious selection by breeders, that this character has 

 become perfectly true and stable in some strains. As pointed out in 

 the earlier portion of this paper, we are restricting our remarks for 

 the present to the consideration of the Mendelian inheritance of 

 certain characters, and that theory seems to fit in well with the 

 main lines of inheritance as borne out by the facts. JS'one the less 

 it is equally evident that there are other factors at work, which 

 are able to modify to some extent the results anticipated by the 

 Mendelian hypothesis. In addition to these definite matings we 

 have also notes of 6 matings Chequer to pure colour (Exps. 164- 

 168, 173) which gave 19 birds all chequered. In this latter set 

 of matings most of the Chequered parents were birds used in or 

 bred from the Chequer to Chequer matings ; and therefore this 

 adds further proof that all those birds were homoz^^'gous 

 dominants, as otherwise we should have expected some self- 

 coloured birds to appear as they did in Exps. 174-203 (p. 606). 



It may be as well to mention here that although some of the 

 matings referred to in this paper were not undei'taken with the 

 special purpose of bringing out the facts which they are used to 

 interpret, yet they have all been conducted by one of the authors 

 in person. Special matings have, however, laeen made in every 

 case to prove the inhei-itance of the characters discussed *'. 



Grizzling. 



Grizzling is dominant to Chequering and hence also to pure 

 colour. It probably originated from the cross between Blue and 

 White, although such matings usually give splashed birds, owing 

 probably to the true Grizzle character, in which individual barbs 

 show both white and blue, being absent. Cases, however, are 

 known in which the cross between pure White and pure Blue 

 have produced Grizzles, and in these cases thei-e is little doubt 

 that the Grizzle character must have been present in one or both 

 of the pai-ents but was unable to show itself owing to the bird 

 containing only one colour. Once, howe\'er, the Grizzle has shown 

 itself, the White and Grizzle characters seem to combine together 

 and to have a common inheritance. Furthermoi'e, as already 

 stated. Grizzles when bred together tend usually, but not 

 invariably, to show an increase of white in successive generations 



* Mr. W. Bateson has stated (Mendel's Principles of Hevedit}-, p. 43 (1909J) that 

 chequering is dominant to its absence ; on writing to him for a reference to the 

 source of his statement, he saj's that he had in mind some experiments of Mr. Staples- 

 Browne, which have, however, not been published. 



43* 



