THE PHENOMENA OF MUTATION 170 



could be combined with the coloured plumage of the 

 type known as black-red. At the same time it must 

 be borne in mind that since the factor, whether a 

 portion of a chromosome or not, is transmitted in 

 heredity as a part of a single cell, the gamete, and 

 since every cell of the developed individual is 

 derived by division from the single zygote cell 

 formed by the union of the two gametes, the factor or 

 determinant must be contained in every cell of the 

 soma, except in cases where differential division, or 

 what is called somatic segregation, takes place. 

 Thus the factor which causes the comb to be a rose 

 comb in a fowl must be present in the cells that 

 produce the plumage or the toes or any other part of 

 the body. Morgan, as mentioned above, finds in 

 Drosophilii that factors do affect several parts of the 

 body. It is, however, curious to consider that the 

 factor which produces intense pigmentation of the 

 skin and all the connective tissue in the Silky fowl 

 has no effect on the colour of the plumage in that 

 breed, which is a recessive white. The plumage is 

 an epidermic structure, and therefore distinct from 

 the connective tissue, but it is difficult to understand 

 why a pigment factor though present in every cell 

 has no effect on epidermic cells. 



The Mendelians, when the mutations of (Enothrra 

 were first described, endeavoured to show that they 

 were merely examples of the segregation of factors 

 from a heterozygous combination. They suggested 

 in fact that (Enothera Lamar ckiana was the result 

 of a cross, or repeated crosses, between plants 

 differing in many factors, that the numerous muta- 

 tions were similar to the variety of different types 

 which are produced by breeding together the grey 



