SWEET PEA ' AUDREY CRIER. 



1-37 



them; 'affects tlie yellow cliromoplasts ; wlien it is dominant (X) these are 

 absent, when recessive (x) they are present and give a yellow tinge to tho 

 flower. 



Audrey Crier is the result, as we have seen, of crossing a pure white, 

 Dorothy Eckford, with a blue-pink on a white ground, Countess Spencer, 

 and its colour is a pink flushed with yellow, making it a salmon-pink. This 

 vellow tinge is evidently not present in Countess Spencer, so it must have 

 been brought in by Dorothy Eckford. The question then arises. Is this 

 yellow tinge due to x or y ? Evidently it is not due to x, if it were, Dorothy 

 Eckford would be a cream, i.e. Mrs. Collier, for the albino form of flowers 

 containing the yellow chromoplasts is cream-coloured. So this yellow 

 flush in Audrey Crier must be due to the factor y in Dorothy Eckford, and 

 as the latter always breeds true to white it must be homozygous for X. 



Knowing that Miss Willmott often throws an albino indistinguishable 

 from Dorothy Eckford, I wrote to Mr. Eckford, to make assurance doubly 

 sure, and he very kindly told me that my surmise was correct, and that 

 Dorothy Eckford was the albino form of Miss Willmott, which latter may 

 be considered the grandiflora form of Helen Lewis. 



Mr. and Mrs. Tpioday found among their seedlings a pea of this colour 



with the factorial composition yyD^xx (omitting C and R). Now 



Dorothy Eckford cannot be recessive for x, nor heterozygous, for it always 

 breeds pure white. Consequently, I take the factors of this pea to te 

 yyDDXX, and further as it is white, either C or R must be absent, pro- 

 bably C, I think. So the complete formula of Dorothy Eckford will be 

 ccRRyyDDXX. 



Mr. and Mrs. T hod ay find the composition of a blue-pink pea to be 

 Y D X • • 



•Y X^ , omitting C and R, both of which must be present. I have 



therefore taken the formula of Countess Spencer as YyDDXx, or includirg 

 C and R, CCRRYyDDXx. 



As both flowers are thus homozygous for D and R we need not take 

 them further into consideration, and if we bear in mind that the F, genera- 

 tion is heterozygous for C, and that consequently we shall get 25 per cent, 

 of whites in F2 we can omit C from our formula in future, leaving only 

 X and Y. 



f Now it is obvious that the Fj generation will be heterozygous for X 

 and Y and, as we have seen above, the colour of the flowers in this genera- 

 tion is the same as that of Audrey Crier. Consequently, we may safe'y 

 assume that those plants which are heterozygous for X and Y will bear 

 flowers of this colour. 



Taking these two factors X and Y respectively, we know that y im- 

 parts a yellowish tinge to the sap of those flowers which are homozygous 

 for it, consequently all such flowers will in F.2 be the colour of Audrey 

 Crier ; we also know that the development of the yellow plastids occurs 

 only in those that are homozygous for x. These plastids, also, give a 

 yellow tinge to those flowers that are homozygous for x, so that they too 

 will be the same colour as Audrey Crier. 



To sum up, three different sets of factors give this colour: 1, YyXx ; 



2, yyXf ; 3, Y^xx. 



