120 Shull. 



individual genes have not been identified? To avoid confusion from 

 this inability to decide whether in any case we are dealing with poly- 

 mery or not, I will distinguish in what follows, between "duplicate" 

 determiners and "plural" determiners for any given character. These 

 two terms must still be understood as making absolutely no assumption 

 regarding the nature or identity of the genes themselves. By "dupli- 

 cate" determiners I understand those which, when separated from each 

 other, produce characters so like that they can not be distinguished 

 from one another; e. g., if P and R are duplicate determiners and XX 

 the residual genotypic "nucleus", then XXPPrr will be indistinguishable 

 from XXppBR and from XXPpEr. By "plural" determiners I shall 

 indicate two or more genes which independently produce a given 

 character, or which, modify it in any way whatever, which does not de- 

 stroy its identity. "Plural" determiners thus also include "duplicate" 

 determiners, of course. In this sense the above mentioned hypothetical 

 genes, N and L, for the internode-number and internode-length, respec- 

 tively, are "plural" genes for plant-height, though by no means 

 "duplicate" genes. This distinction has not been clearly made by 

 writers who have discussed the Mendelian inheritance of quantitative 

 characters, and as such discussions have invariably taken as their point 

 of departure, cases in which duplicate determiners have been demon- 

 strated, there has always been a more or less obvious implication, if 

 not a direct statement, that in the inheritance of these various quanti- 

 tative characters, duplicate determiners are involved. 



The consequences which result from the existence of duplicate 

 determiners for single characters, have been so well discussed by 

 NILSSON-EHLE (1908, 1909, 1911), EAST (1910, 1912), LANG (1910, 

 1911), EMERSON and EAST (1913) and others, that it may suffice to 

 indicate here the characters for which duplicate determiners, or at least 

 plural determiners > >/have been demonstrated (in full-faced type), and 

 those incompletely analyzed characters for which, as a sequel to the 

 discovery of duplicate determiners, a plurality of Mendelian genes has 

 been assumed to exist. The following list is believed to be fairly com- 

 plete for the cases in which relevant data are given, or definitely re- 

 ferred to. In some of the more enthusiastic statements regarding the 

 importance of plural Mendelian genes, suggestions of their applicability 

 to other cases have been made, as, e. g., in EAST'S interpretation 

 (1912) of hybridization phenomena in Oenothera, but such cases are 

 not here included. 



ADD: which according to present evidence appear 

 to b duplicate, 



