ON PHYSIOLOGICAL CHROMOMERES. 



From almost all the other species, varieties, monstrosities and 

 hybrids, which now constitute the material for genetical studies, 

 the mutations of (Enothera Lamarckiana are well known to differ 

 in one main point. Most of them appear in relatively large groups 

 of characters, from which it is difficult to isolate and determine 

 the single factors. They must be due to complexes of factors or 

 complex factors, as it is often called. Each of these groups changes 

 the whole aspect of the plant and the differences are of the same 

 rank as those, on which in our descriptive works the diagnoses of 

 species are usually founded. 



Of course, besides these typical mutations, some of the ordinary 

 kinds are seen to occur. In drawing a parallel with other organisms 

 one is often inclined to put these upon the foreground, especially 

 since some of them are among the commonest occurrences as, e. g., 

 the dwarfish stature and the brittle stems. But they are not special 

 to the (Enotheras and are, as a rule, more easily studied in other 

 organisms. They only tend to obscure the real meaning of the main 

 phenomenon. 



On the basis of the theory of Morgan we must assume that the 

 factors for each of these groups of mutations are located in distinct 

 regions of the chromosomes, neighbourhood being a necessary con- 

 dition for such linkages. On the other hand the groups are trans- 

 mitted regularly as such from each generation to the next, thus 

 constituting undubitable, although compound units. Such parts of 

 the chromosomes may here be designated as physiological chromo- 

 meres, at least provisionally, until we may succeed in discerning 

 them cytologically. 



There are seven chromosomes in the haploid nuclei of our evening 

 primroses, three of them being larger than the others. Among the 

 typical mutants there are six old types, which have been described 

 as dimorphic mutants. Two of those have constituted, since the 

 very beginning of my researches, the main point of interest, around 

 which the others were distributed. They were called 0. mut. lata 

 and 0. mut. scintillans. 



Almost exactly parallel to these in their hereditary behaviour, 



