As these orchids had grown under unnatural conditions, in {134} hot-houses, I concluded without hesitation that their self-sterility was due to this cause. But Fritz Mueller informs me that at Desterro, in Brazil, he fertilised above one hundred flowers of the above-mentioned _Oncidium flexuosum_, which is there endemic, with its own pollen, and with that taken from distinct plants; all the former were sterile, whilst those fertilised by pollen from any _other plant_ of the same species were fertile. During the first three days there was no difference in the action of the two kinds of pollen: that placed on the stigma of the same plant separated in the usual manner into grains, and emitted tubes which penetrated the column, and the stigmatic chamber shut itself; but the flowers alone which had been fertilised by pollen taken from a distinct plant produced seed-capsules. On a subsequent occasion these experiments were repeated on a large scale with the same result. Fritz Mueller found that four other endemic species of Oncidium were in like manner utterly sterile with their own pollen, but fertile with that from any other plant: some of them likewise produced seed-capsules when impregnated with pollen of widely distinct genera, such as Leptotes, Cyrtopodium, and Rodriguezia! _Oncidium crispum_, however, differs from the foregoing species in varying much in its self-sterility; some plants producing fine pods with their own pollen, others failing to do so; in two or three instances, Fritz Mueller observed that the pods produced by pollen taken from a distinct flower on the same plant, were larger than those produced by the flower's own pollen. In _Epidendrum cinnabarinum_, an orchid belonging to another division of the family, fine pods were produced by the plant's own pollen, but they contained by weight only about half as much seed as the capsules which had been fertilized by pollen from a distinct plant, and in one instance from a distinct species; moreover, a very large proportion, and in some cases nearly all the seed produced by the plant's own pollen, was embryonless and worthless. Some self-fertilized capsules of a Maxillaria were in a similar state.