Theory of Plant Breeding 



another suggested explanation. Probably the original 

 seed colour was green, and yellow has been formed 

 because the plastids in certain more advanced races have 

 stopped at the yellow stage of development, and not 

 gone on to the formation of green. This yellow is then 

 a progressive step in the evolution of a species, and 

 would be, according to Davenport's view, likely to be 

 dominant. 15 But according to Emerson (U.S.A. Exp. 

 St., Nebraska, 1902), one also finds in racial hybrids 

 of kidney beans both new colours, and others which 

 seem to result from some very distant ancestor (atavistic). 



One very common theory amongst practical breeders, 

 viz., that the pollen parent decides the flower colour of its 

 descendants, seems not to be substantiated by experiment. 



Chittenden found that of 183 hybrids, 42 were of 

 the male colour, 46 of the female; 92 were intermediate, 

 and 3 were unlike both ancestors. 16 But although, as 

 the reader will have realised already, Mendel's results will 

 be of great service in practice, they must not be considered 

 as all-important. Macfarlane has clearly shown that cer- 

 tain hybrids do not follow Mendelian laws, but form a 

 series of transitions between the colours of their parents. 



So far as Mendel's laws bear upon evolution they 

 bring out clearly two facts first, that such characters 

 as colour are clearly inherited, which has an important 

 bearing upon the inheritance of acquired characters ; 

 and, secondly, that it is unlikely that hybridising can 

 have played any important part in the formation of new 

 species. The tendency in hybrids seems to be for them 

 to work back to the original parent types. 



But even these conclusions are somewhat uncertain. 

 The genus Iris has three stamens only, and one would 

 think that this was an absolutely fixed character. Some 

 very distant ancestor no doubt had six stamens, for that 

 is almost universal in all allied orders. But Heinricher 

 discovered occasional extra stamens in about 18 per 



35 u 



