474 COBB AND BARTLETT: INHERITANCE IN OENOTHERA 



of the genetical peculiarities of Oenothera^^ (see also footnote 6), 

 the male gametes of all of the mutations concerned are 

 thought of as (3 gametes, and as exactly like the (3 gametes of the 

 particular f. typica from which each mutation was derived. It 

 has been assumed that the appearance of mutations showing 

 matroclinic inheritance in crosses with the parent form is due to 

 changes involving the a gametes, which bear various factors not 

 represented in the gametes. Such mutations constitute the 

 greater number of those derived from Oenothera pratincola. 

 They appear as the result of some modification of the uncom- 

 pensated factors of the generally female a gametes, and therefore 

 breed true from the first. The generally male /S gametes of Oe. 

 pratincola have as yet given rise to no mutations that have been 

 detected, but de Vries^'' has found that one of the mutations of 

 Oenothera biennis (var. suljured) shows patroclinic inheritance 

 in crosses with its parent, and is therefore presumably such a 

 mutation. In the heterogametic species of Oenothera, muta- 

 tions involving the uncompensated factors of the a gametes 

 obviously cannot show Mendelian inheritance. If the a gametes 

 are female, inheritance must be matroclinic. 



Since such a conception as that of a series of different muta- 

 tions, or even of different species, in which the differentiation 

 is brought about wholly by the female gamete, is justifiably 

 foreign to current thought, it may be well to restate some of 

 the grounds for its adoption. 



It is a fundamental tenet of Mendelism that in homozygous 

 material the two homologues chromosomes of each pair are equiva- 

 lent and interchangeable. In heterozygous material one or more 

 chromosomes are modified, but still remain interchangeable with 

 their mates. If the uncompensated characters of the a gamete 

 were borne in one chromosome, the only essential difference that 

 would obtain between the conceptions of heterozygosis and of 

 heterogametism would concern the unequal distribution of a. 



1^ Bartlett, H. H. The status of the Mutation Theory, with especial reference 

 to Oenothera. Amer. Nat. 50: 513—529. 1916. 

 1^ DE Vries, H. Gruppenweise Artbildung, p. 298. 



