Shull. 



pastoris from different regions, and hope to be able at a later date to 

 give further data bearing upon this question. 



As we have already seen, the simple shifting of a chromosome 

 carrying the determiner for the triangular capsule into a new position 

 with reference to the other chromosomes probably gave rise to the recessive 

 mutant B. Heegeri, a result which has been generally referred heretofore 

 to the "loss" or "destruction" of a determiner. It is an attractive hypoth- 

 esis that such shifting of determiners may account for the occurrence of 

 recessive mutants generally, as well as to some dominant mutants, but 

 it is a hypothesis which I believe incapable of more than a very limited 

 application, for the simple reason that retrogressive mutation is a rel- 

 atively frequent phenomenon, while duplication of determiners is, so 

 far as present evidence indicates, a relatively infrequent one. If both 

 phenomena were due generally to the same cause they should appear 

 with similar frequency. The suggestion of EMERSON and EAST (1913, 

 p. 13) that it is "quite within the range of possibility that some of 

 DE VEIES'S Oenothera mutants have originated" from the union of germ- 

 cells having duplicate Mendelian determiners for the parental charac- 

 teristics, none of these duplicate genes happening to occupy homologous 

 positions in both germ-cells, can not be accepted by any one familiar 

 at first hand with the genetic phenomena in the genus Oenothera, A 

 consequence of such an interpretation would be that plants should often 

 be found whose progeny produced by self-fertilization would consist 

 of 75 per cent of the parent- type and 25 per cent of the particular 

 mutant -type. From hundreds of such self-fertilizations which have 

 been made among the "mutating Oenotheras", with strictly individual 

 analysis, no such result has been secured. The total number of mutants 

 of all types has rarely exceeded 5 7 per cent. Attempts to interpret 

 the genetic behavior of the Oenotheras on a Mendelian basis or to 

 apply experiences with Oenotheras to other groups in which Mendelian 

 inheritance has been demonstrated, is still premature. A great deal of 

 purely inductive work on this genus will be required before it can be 

 safely articulated genetically with other groups. 



The data presented in the present paper removes the duplication 

 of genes of the triangular capsule in Bursa from the status of a mere 

 interpretation to one of complete demonstration. Although this has 

 required considerable labor, it has been accomplished with ease compared 

 with the work which will be necessary to demonstrate the truth or 

 falsity of the proposition that plural Mendelian determiners adequately 

 explain any case of a) the inheritance of apparently continuous quan- 



