HYBRID OF DIGITALIS. 371 



•qualities or powers may be called factors, and the factorial 

 hypothesis attempts to give some explanation of the nature and 

 transmission of factors in sexual and asexual reproduction. 

 Mendelism is merely a certain aspect of the factorial hypothesis, 

 and one of the main points of dispute is, whether factors are to be 

 o-enerally regarded as essentially fixed and unchangeable, so that, 

 when segregation occurs, the pure factor emerges uninfluenced by 

 its former association with other factors or by the external environ- 

 ment. It is important to note that evidence has been recently 

 brought forward by Professor Bateson indicating that segregation 

 •can occur in other cells than in germinal cells. 



In a previous paper already cited the behaviour of crosses of 

 varieties of a species was discussed, and it was shown that in all 

 those characters capable of measurement which were examined the 

 degree of development was inherited in self -fertilised generations, 

 and, on crossing, a blend occurred in the offspring. The factors 

 controlling these characters were also blended, since in subsequent 

 generations raised by self-fertilisation there was no tendency for a 

 reappearance of the grandparental characters in an unchanged 

 condition. 



A point of some interest may be mentioned. The peloric 

 character of foxgloves, like the purple colouration, is inherited in 

 a perfectly typical Mendelian fashion. But there are all degrees 

 of pelorism, just as there are of colour intensity, and the inherit- 

 ance of the degree of pelorism and of the intensity of colour is of 

 the blended type. With blended inheritance, selection is effective 

 in producing a gradual modification; but on account of the lack 

 of sufficient variation combined with the drag of regression it may 

 not always be possible to carry the modification to any great 

 •extreme. 



By regression is meant the influence whereby exceptional 

 parents tend to produce offspring which are more normal (that is 

 •closer to the mean of the race) than themselves. The existence of 

 regression, in the sense in which Galton used the term, as the drag 

 of the back ancestry, has been denied by some. It is stated by 

 Babcock and Clausen 1 "this regression is not due to the pull of 

 .a back ancestry ; it is due to the fact that individuals whose somatic 

 appearance places them in diverse classes in the frequency distribu- 

 tion are themselves gametically different and will breed differ- 

 ently." 



The statement in italics is doubtless true, and the breeding 

 differently is due to the factors being different, arising from 

 the fact that the powers of any individual factor in producing a 

 somatic character must depend on the constitution of that factor, 

 and the particular nature of any individual factor is the result 

 of its past history which involves the back ancestry. 



Such a view is not compatible with the assumption of discrete 

 and relatively unchangeable factors, and hence is rejected by the 



'Babock, E. B., and Clausen, E. E. " Genetics in relation to Agriculture," 

 1918, p. 55. 



