CHAP. VII. POLYGAMOUS PLANTS. 287 



bearing long stamens exserted beyond the corolla, 

 has been converted into the male ; and a long-styled 

 progenitor with fully developed stigmas into the fe- 

 male. 



From the number of bad pollen-grains in the small 

 anthers of the short stamens of the long-styled form 

 of Pulmonaria angustifolia, we may suspect that this 

 form is tending to become female; but it does not 

 appear that the other or short-styled form is becoming 

 more masculine. Certain appearances countenance 

 the belief that the reproductive system of Phlox subu- 

 lata is likewise undergoing a change of some kind. 



I have now given the few cases known to me in 

 which heterostyled plants appear with some consider- 

 able degree of probability to have been rendered 

 dio3cious. Nor ought we to expect to find many such 

 cases, for the number of heterostyled species is by no 

 means large, at least in Europe, where they could 

 hardly have escaped notice. Therefore the number of 

 dioecious species which owe their origin to the trans- 

 formation of heterostyled plants is probably not so 

 large as might have been anticipated from the facilities 

 which they offer for such conversion. 



In searching for cases like the foregoing ones, I have 

 been led to examine some dioecious or sub-dioecious 

 plants, which are worth describing, chiefly as they 

 show by what fine gradations hermaphrodites may 

 pass into polygamous or dioecious species. 



Polygamous, Dioecious and Sub-dioecious Plants. 



Euonymus Europeeus (Celastrineae). The spindle-tree 

 is described in all the botanical works which I have 

 consulted as an hermaphrodite. Asa Gray speaks of 

 the flowers of the American species as perfect, whilst 



