I have now given the few cases known to me in which heterostyled plants appear with some considerable degree of probability to have been rendered dioecious. 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 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 dioecious species. POLYGAMOUS, DIOECIOUS, AND SUB-DIOECIOUS PLANTS. Euonymus Europaeus (CELASTRINEAE). (Figure 7.12. Euonymus Europaeus Left: Hermaphrodite or male. Right: Female.) 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 appearance well developed. The other half have a perfect pistil, with the stamens short, bearing rudimentary anthers destitute of pollen; so that these bushes are females. All the flowers on the same plant present the same structure. The female corolla is smaller than that on the polleniferous bushes. The two forms are shown in Figure 7.12. I did not at first doubt that this species existed under an hermaphrodite and female form; but we shall presently see that some of the bushes which appear to be hermaphrodites never produce fruit, and these are in fact males. The species, therefore, is polygamous in the sense in which I use the term, and trioecious. The flowers are frequented by many Diptera and some small Hymenoptera for the sake of the nectar secreted by the disc, but I did not see a single bee at work; nevertheless the other insects sufficed to fertilise effectually female bushes growing at a distance of even 30 yards from any polleniferous bush.