MENDELISM AND SEX 131 



nature which we are now considering will resolve 

 itself into the simple Mendelian one of D R by 

 RR.^ The DR here represents the male plant 

 and the R R the female plant. The symbol D 

 in this case stands for maleness, which is dominant, 

 and R for femaleness, which is recessive. Since the 

 female plant bears only "^ female " egg-cells and the 

 male plant bears both ''male" and "female" pollen- 

 cells in equal numbers, it must happen in the random 

 meetings resulting from pollination that one-half of 

 the "female" egg-cells will be fertilised with " male" 

 pollen-cells which will give us D R offspring, and 

 one-half with " female " pollen-cells which will 

 give us R R offspring. And, since maleness is 

 dominant, then the individuals which result from a 

 fertilisation of R egg-cells by D pollen-cells will 

 be hybrids and will be visibly male. Thus there 

 will be produced equal numbers of hybrid males 

 {D R's) and of pure females [R R's). So far, then, 

 the Mendelian interpretation is in accordance with 

 the experimental facts, and it gives them an in- 

 telligible unity. 



Let us pass next to consider the crosses between 

 the two different species. As we have already seen, 

 they resolve themselves into crosses of the two 

 following kinds : — 



Nature of Cross. 

 Bryonia Dioica. x Bryonia Alba. Result. 



(Unisexual). (Hermaphrodite). Offspring. 



(1) Flowers of female plant x Male flowers = All females 



(2) „ ., male „ x Female flowers = Males and females 



* See page 69, where such a cross is explained. 



