332 THE BIOLOGY OF FLOWERING PLANTS 



(19 1 9) in a study of Salix amygdaloides found 9 per cent, of 

 the individuals to bear catkins which are male below and 

 female above, with a zone of hermaphrodite flowers in 

 between ; in Moms albus, he found 20 per cent, of inter- 

 mediate individuals. We have already mentioned the case 

 of Mercurialis annua in which male plants occasionally bear 

 female flowers and vice versa. It is probable that all 

 diclinous species may at one time or another exhibit such 

 irregularities. In species with more than one type of flower 

 on the individual the intergrades are most frequent. A 

 general review of this subject will be found in Yampolsky 

 (1920). 



§ 6. Determination of Sex 



The ordinary type of angiosperm with hermaphrodite 

 flowers must possess in the inheritance of each individual 

 the potentialities of both sexes, since it does in fact bear both 

 male and female organs. Here the separation of the sexes, 

 to whatever it may be due, is somatic, and occurs when the 

 stamens and carpels come to be laid down at diff^erent points 

 of the meristematic zone of the same flower rudiment. Even 

 there derangement may set in ; teratological flowers are 

 known in which stamens bear ovules, e.g. in Sempervivum, 

 or carpels produce pollen, e.g. in Begonia. In simply 

 moncecious plants the same thing is true. Each individual 

 can and does produce both types of sexual organ ; the 

 separation may take place when the flowers or inflorescences 

 are developing, or it may occur earlier in the individual 

 development in plants where one type of flower constantly 

 occupies a definite place on the axis. In Sagittaria the 

 male flowers are always borne higher than the female ; in 

 the maize the male inflorescence is terminal, the female is 

 axillary. 



In dioecious species we might be tempted to believe that 

 some individuals inherit only maleness and others only 

 femaleness ; or, in the more complex cases, that some 

 inherit one sex and others both. A little consideration 



