CHAP. VII. POLYGAMOUS PLANTS. 287 



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 mascu- 

 line. Certain appearances countenance the belief that 

 the reproductive system of Phlox subulala 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 dioe- 

 cious. 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 spe- 

 cies which owe their origin to the transformation 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 difficious species. 



Polygamous, Dioecious and Sub-dioecious Plants* 

 Euonymus Europceus (Celastrinese). 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 

 those in the allied genus Celastrus are said to be 

 " polygamo-dioecious." If a number of bushes of our 

 spindle-tree be examined, about half will be found to 

 have stamens equal in length to the pistil, with well- 

 developed anthers; the pistil being likewise to all ap- 



