V] Dominant IVhites 105 



The facts thus take their places in a consistent scheme, 

 and when the factors are correctly determined, all the 

 observed properties of the several types can be represented. 

 Some curious consequences follow which would have ap- 

 peared very surprising both to evolutionists and to fanciers 

 a few years ago. For example, if a pair of coloured birds 

 throw very few whites the chances are large that these 

 whites if mated together will breed true. On the other 

 hand if a pair of coloured birds throw many whites, the 

 chances are that such whites if bred together will have 

 some coloured offspring, and it is not very unlikely that all 

 their offspring will be coloured ! For in the first case where 

 the whites are few, they are probably i in 4, indicating 

 that both parents are homozygous in either X or K, say X, 

 and heterozygous in respect of the other factor Y, There- 

 fore all the whites which come will be carrying X and none 

 will have Y. Therefore they will breed true to whiteness 

 if mated together. 



In the second case however, where the whites are 

 many, they are probably 7 whites : 9 coloured. In such 

 a case the parents must be heterozygous both in X and in 

 Y. Consequently some of the whites will be bearing X 

 and others K, and there will be a good chance that if such 

 whites are bred together these two complementary factors 

 will again come into combination and coloured offspring be 

 produced. 



Among plants only one example of dominance of white 

 flower-colour over the ordinary sap-colours has yet been 

 investigated. This occurs in Primula Sinensis. In this 

 species colour may be present either in the flowers, or in 

 the stems and leaves, or in both. When white flowers 

 occur on stems green and devoid of pigment, the white is 

 recessive as in any other case of total albinism. There are 

 however white varieties which have more or less red in 

 the stems, and these when crossed with varieties having 

 coloured flowers give F^ with flowers white or nearly so. 

 There is almost but not quite always a slight tinge of 

 magenta-red in the petals of such F^ plants, and the in- 

 tensity of this colour increases with low temperatures but 

 diminishes if the house be kept warm. 



Such dominant whites, when crossed with the green- 



