130 THE MENDEL JOURNAL 



female B. dioica are crossed with those of a male B. 

 dioica, the offspring consist of a mixture of male and 

 female plants. 



The most interesting crosses, however, are the 

 reciprocals between the hermaphrodite plant of 

 B. alba and the two unisexual plants of B. dioica. 

 When the flowers of the female plant of B. dioica 

 are crossed with the male flowers of B. alba, all the in- 

 dividuals in the offspring are female plants.* But 

 the reciprocal cross, strangely enough, gives a very 

 different result. For, when the female flowers of 

 B. alba are pollinated with pollen from the flowers 

 of a male B. dioica, the offspring consist of male 

 and female plants in approximately equal numbers. 



Correns endeavoured to interpret these results 

 in the following way. Let us take first the cross 

 of male B. dioica with female B. dioica. The result, 

 as we have seen, is a mixture of males and females 

 in equal numbers. We will for the moment assume, as 

 Correns did, that maleness is dominant ; that the male 

 plants are Mendelian hybrids and therefore carry two 

 kinds of pollen-cells in approximately equal numbers, 

 one half bearing the character of maleness and the 

 other half that of femaleness ; and that the female 

 plant, being recessive, must be pure with regard to 

 femaleness, and all its egg-cells will therefore carry 

 femaleness alone. It is clear that a cross of the 



*A few exceptions — 2 males with 589 females — are said to occur, 

 and a few of the females bear occasional male flowers. 



