278 DKECIOUS AND CIIAP. VII 



CHAPTER VII. 



POLYGAMOUS, DICECIOUS, AND GYNO-DKECIOUS PLANTS. 



The conversion in various ways of hermaphrodite into dioecious plants 

 Heterostyled plants rendered dioecious Rubiacess Verbenactaa 

 Polygamous and sub-dicecious plants Euonymus Fragaria 

 The two sub-forms of both sexes of Ehamnus and Epigaea Ilex 

 Uyno-dicecious plants Thymus, difference in fertility of the her- 

 maphrodite and female individuals Satureia Manner in which 

 the two forms probably originated Scabiosa and other gyno- 

 dicecious plants Difference in the size of the corolla in the forms 

 of polygamous, dioecious, and gyno-dicecious plants. 



THERE are several groups of plants in which all the 

 species are dioecious, and these exhibit no rudiments 

 in the one sex of the organs proper to the other. 

 About the origin of such plants nothing is known. It 

 is possible that they may be descended from ancient 

 lowly organised forms, which had from the first their 

 sexes separated ; so that they have never existed as 

 hermaphrodites. There are, however, many other 

 groups of species and single ones, which from being 

 allied on all sides to hermaphrodites, and from ex- 

 hibiting in the female flowers plain rudiments of 

 male organs, and conversely in the male flowers rudi- 

 ments of female organs, we may feel sure are descended 

 from plants which formerly had the two sexes com- 

 bined in the same flower. It is a curious and obscure 

 problem how and why such hermaphrodites have been 

 rendered bisexual. 



If in some individuals of a species the stamens 

 alone were to abort, females and hermaphrodites would 



