MENDELISM AND SEX 129 



male as a pure recessive, or vice versa, then they 

 will be respectively symbolised SiS D R and R R. 

 A reference to the table of matings on page 69 will 

 show that the expected offspring from 3, D R parent 

 mated with a,n R R one, will consist in equal numbers 

 of D R's, which in this case will be females — if we 

 regard the female character as dominant — and of 

 R i?'s, which will be males. Thus far, then, the 

 two general facts already known to us, namely, the 

 segregation and numerical equality of the sexes, 

 strongly suggest that sex is predestined in the germ- 

 cells and is hereditarily transmitted in accordance 

 with the Mendelian principles of gametic purity and 

 segregation. 



It was not however until quite recently that experi- 

 ments specifically designed to answer the questions 

 presented by sex have, by their results, extended the 

 suggestion into proof. Among the most important 

 and interesting of such experiments we must place 

 those of Professor Correns with two species of the 

 Bryony plant. In the species known as Bryonia 

 dioica female flowers are found on one plant 

 and male flowers on another ; the two sexes are 

 borne on different individuals, so that any particular 

 plant is either male or female, and not hermaphrodite 

 like the majority of plants. The other species, 

 named Bryonia alba, has the sexes borne on different 

 flowers but on the same plant. Each individual 

 plant is therefore hermaphrodite, bearing both male 

 flowers and female flowers. When the flowers of 



