Duplicate genes for capsule-form in Bursa barsa-pasloris. ] 19 



phenomenon in o-cneral, the latter for those; cases in whicli there is 

 complete dominance and no cumulative effect produced h\- the presence 

 of several genes for the character in question, as compared with the 

 presence of but one. To the genes themselves which independently 

 produce the same or similar effects, Lang applies the name "genomeres". 

 The demonstration of the phenomenon, or rather the phenomena, 

 which have suggested these new words, marks an important advance in 

 genetic progress, because it has led to a fairly well grounded Mendelian 

 interpretation of inheritable ciuantitative characters, which have often been 

 cited as offering fundamental exceptions to the Mendelian principles. There 

 is some danger, however, that this assignment of names will give a 

 wrong impression as to the nature and unity of the phenomena foi' which 

 they have been suggested. The fact must never be lost sight of that 

 the real nature of the genes is purely inferential, since we can know 

 nothing of them except through the morphological or physiological effects 

 which they produce. Two determiners producing or affecting a given 

 character may be identical, slightly different, or profoundly different, 

 from each other, and the question is likely to arise over and over again 

 as to whether any given character represents a case of polymery or not. 

 Thus, we may assume, merely as an illustration, that a plant has its 

 number of internodes determined by a Mendelian gene N and the length 

 of the internodes by another independent determiner L. Are these to 

 be considered "genomeres" in the sense of Lang? One can scarcely 

 think so, and yet these two elements make up the height of the plant 

 in question, and plant -height is one of the characters for the expla- 

 nation of whose hereditary behavior polymery has been assumed ' ) ! 

 Or are we to speak of "polymery" only when the effects of the 



') The reader is also urged to read the valuable paper by H.vgedoorn (li)I4) 

 which appeared after the present paper was in press. No change has been made in the 

 present paper except the inclusion of Hagedoorn's paper in the references, and the 

 addition of this footnote. It will be seen that my views and Hagedooun's are in 

 complete harmony; on a number of points there is a close parallel between his discussion 

 of plural determiners and mine. There are several points, however, in which I do not 

 fully agree with him. I see no good reason, for instance, for abandoning the use of 

 the expression "unit-characters", nor for giving up the system of symbols for the genes, 

 which suggests, whenever it can be conveniently done, some characteristic reaction in 

 which the gene in question takes a critical part. The abandonment of this method 

 tends to make the results of genetic research more inaccessible. With proper emphasis 

 upon the real relation between the determiners and the unit-characters, the suggestive 

 symbol can lead to no more serious misapprehension than that which results from the 

 use of any symbol whatever. 



