Duplicate genes for capsule-form in Bursa bursa-pastoris. ____ 135 



external environment. This "rest of the genotype" may be the deter- 

 mining factor in producing the correlations. It is probable that the 

 correlations found by TAMMES represent in large measure, if not wholly, 

 the phenomenon long known as physiological correlation, and recently 

 designated by BALLS (1911) "autogenous fluctuation". An individual 

 is not a mosaic of independent parts, but a unit made up of members 

 and characteristics which are often independent from each other in 

 inheritance, but which are largely dependent upon each other in devel- 

 opment. If the correlation of these characters is not simply due to 

 their somatic interdependence it is much more plausible to assume that 

 some of the plural determiners which affect one of these characters 

 are also among the plural determiners which modify one or more of 

 the other characters, and that all of these determiners are inherited 

 independently according to the simple Mendelian method, than to assume 

 that there is a complex coupling of some sort, resulting in gametic 

 series such as 3 : 1 : 1 : 3, 7:1:1:7, &c., instead of the usual 1:1:1:1. 

 When we begin to speculate regarding the genotypic basis for 

 the plural determiners, it is of the greatest importance that the rela- 

 tively rare phenomenon of duplication of determiners be not confused 

 with the nearly universal occurrence of non- duplicate plural determiners. 

 There is nothing special in the history or the genotypic interpretation 

 of the latter, their peculiarity in affecting the same organ or other 

 character of an organism, is purely an incident of somatic physiology, 



- a "physiological correlation", - - and therefore, any discussion of 

 the genotypic basis of such complex characters must be simply a con- 

 sideration of the material basis for the Mendelian behavior in general, 



- a subject whose adequate discussion can not be undertaken here. 

 The actual duplication of Mendelian unit-characters, on the other hand, 

 deserves some special consideration because in these there is some 

 likelihood that the cause for the duplication may involve, at least in 

 some cases, a series of special genotypic phenomena. 



It may prepare sufficiently for what follows to indicate briefly 

 my attitude toward the question of the material basis of Mendelian 

 characters. The following three propositions may serve this purpose: 

 (1) The observed behavior of the chromosomes is such that if different 

 chromosomes have permanently different functions, these functions must 

 be distributed among the offspring exactly as Mendelian unit-characters 

 are distributed; (2) It is not necessary to assume that the visible 

 chromosomes are the only elements of the cell which partake of the 

 same method of distribution during the processes of reduction, fertil- 



