C. J. Bond 343 



It is a matter of considerable interest to find that two types of 

 abnormal flowers exist in the Begonias : — 



1. The common type in which, round a central more or less per- 

 fectly developed gynoecium, rudimentary organs of the male type occur. 

 (PI. XVI, fig. 7.) 



2. A far less common type in which rudimentary female organs are 

 gathered round a centrally placed androecium. (PI. XVI, figs. 3, 4, 5, 8.) 



Flowers of the first type are here called primarily female. Flowers 

 of the second type are called primarily male. The criterion being the 

 relative position of the male and female sex organs to each other on the 

 common floral axis. 



It is here suggested that the almost universal central and terminal 

 position of the female organs in hermaphrodite flowers is a fact of 

 considerable phylogenetic importance. 



It would seem that the female portion of the flower represents the 

 undifferentiated reproductive rudiment from which the male portion 

 has during evolution segregated off. 



This suggestion receives some support from the frequent (though 

 not invariable) occurrence of vestigial remains, or rudimentary organs 

 of the opposite sex, in the female rather than in the male flower in 

 monoecious and in some dioecious plants. It would be interesting to 

 know how many of these cases in which vestiges of the opposite sex 

 organs are found in the male and not in the female flower represent a 

 return to, rather than a step forward towards, the hermaphrodite form. 

 Further the question of the homozygous or heterozygous nature of the 

 male and the female plant, in respect of sex in the Mendelian sense, 

 assumes additional importance from this point of view. 



Bearing in mind the fact that sex difterentiation is one of the 

 earliest stages in plant, as in animal evolution, and that the difteren- 

 tiation of male and female sex organs on different individual plants or 

 on different parts of the same individual plant, was probably already 

 established in the Cycads, Ginkgos, Sphenophylls and other possible 

 ancestors of our flowering plants, the problem of the sex evolution of the 

 hermaphrodite flower is probably not so much a question of differentiation 

 of sex organs into male and female, as of bringing together into close 

 juxtaposition on one common floral axis, male and female sex organs 

 formally located in different plants or in different parts of the same 

 plant. 



Though the active factor in bringing about the evolution of the 

 hermaphrodite flower was probably a necessity for adaptive capacity on 



