x] Sex in Bryony 167 



sterile, forming no good pollen and failing to set seed 

 when fertilised with pollen of the types. 



Correns (81, p. 27) interprets these facts as meaning 

 that the germ-cells of dioica $ are differentiated in regard 

 to sex, and respectively bear either maleness or femaleness. 

 The male is thus heterozygous in sex, maleness being- 

 dominant. The female dioica is consequently taken to be 

 homozygous in femaleness. The condition of the sexual 

 cells of the monoecious alba is not quite so readily repre- 

 sented. Since dioica $ x alba $ gives plants all ? or with 

 only traces of maleness, the male cells of alba are regarded 

 as all alike undifferentiated in respect of sex, bearing, that 

 is to say, the monoecious character, and presumably the 

 female cells of alba are in the same condition. 



The facts would then be represented thus : 



dioica $ is taken to be $ ?. 



dioica $ ,, ,, $ J, male being dominant. 



alba ? g 



alba $ ,, 



Thus as the results of breeding we have : 



A. dioica $ x dioica $ giving females $ $ and males $ J. 



B. alba $ x dioica $ giving females ? $ and males J g . 



C. dioica $ x alba $ giving all females of the form $ . 



The difficulty in this scheme is that, if maleness were 

 dominant, it is not clear why the plants produced in case 

 C .should be almost entirely females ; for it seems natural to 

 expect that some of the dominance of maleness would 

 attach to the gametes of monoecious character produced by 

 alba, and hence that male flowers should be produced with 

 frequency by the female hybrids. This nevertheless is not 

 the case. In our experiments, out of 37 plants thus bred, 

 34 were purely female and only 3 showed any male flowers. 

 These were in all cases at the lowest flowering nodes. In 

 one plant 4 male flowers occurred in this position, and in 

 each of the other two plants a single male flower appeared. 

 The reciprocal cross, alba ? x dioica $ gave 6 pure females, 

 i lemale with a single male flower, and 9 pure males. 



Correns observed a similar occurrence of male flowers 

 in the same position on the otherwise female hybrids raised 



