No. 585] MODIFICATION OF CHARACTERS. 567 



chromosome pairs. The latter effect may be due to a 

 modification of the chromosomes themselves, or perhaps 

 of the surrounding cytoplasm, or the inhibition in pig- 

 mentation may be explained by the presence of more 

 numerous grandiflora chromosomes. Everywhere, in an 

 accurate study of the inheritance of R, the quantitative 

 as well as the qualitative (presence or absence) aspect 

 has to be considered. 



The dilution effect from crossing back with grandiflora 

 has been tested in six families numbering 673 individuals 

 and is always essentially the same. Although segregation 

 into the E and r types takes place when the parent is 

 heterozygous, yet R once diluted always remains so and 

 apparently never gives rise to the original deeply pig- 

 mented condition. In other words, a permanently blended 

 condition arises as regards the depth of pigmentation, 

 although this will still segregate from the unpigmented 

 condition in heterozygous plants. 



It is not easy to furnish a complete explanation for this 

 diluting effect. The permanent dilution of R through 

 union with a grandiflora germ cell may perhaps be ac- 

 counted for by the fact that in the heterozygote the chro- 

 mosomes of f/rai/di flora arc closely associated in the same 

 nucleus with those of the other parent. The chromosomes 

 which are finally dissociated in the germ cells, after thou- 

 sands or millions of mitotic divisions in association, 

 might then be supposed to be somewhat modified. There 

 are, however, difficulties with this view, since the absence- 

 character, r, is usually not contaminated, but splits out 

 sharply and almost invariably without any trace of red- 

 production. 



It is also difficult to account for the facts on the 

 assumption that the cytoplasm has been permanently 

 modified. 



There is, however, one hypothesis which appears to 

 meet the case. If all the grandiflora chromosomes are 

 equally effective in inhibiting anthocyanin production in 



