Ancient authors, Linnæus, and some later botanists, admitted two species of this fruit tree of the family of Myrtaceæ, the one with elliptical or spherical fruit, with red flesh, _Psidium pomiferum_; the other with a pyriform fruit and white or pink flesh, more agreeable to the taste. Such diversity is also observed in pears, apples, or peaches; so it was decided to consider all the Psidii as forming a single species. Raddi saw a proof that there was no essential difference, for he observed pyriform and round fruits growing on the same tree in Brazil.[1207] The majority of botanists, especially those who have observed the guava in the colonies, follow the opinion of Raddi,[1208] to which I was inclined, even in 1855, from reasons drawn from the geographical distribution.[1209] Lowe,[1210] in his _Flora of Madeira_, maintains with some hesitation the distinction into two species, and asserts that each can be raised from seed. They are, therefore, races like those of our domestic animals, and of many cultivated plants. Each of these races comprehends several varieties.[1211] The study of the origin of the guava presents in the highest degree the difficulty which exists in the case of many fruit trees of this nature: their fleshy and somewhat aromatic fruits attract omnivorous animals which cast their seeds in places far from cultivation. Those of the guava germinate rapidly, and fructify in the third or fourth year. Its area has thus spread, and is still spreading by naturalization, principally in those tropical countries which are neither very hot nor very damp. In order to simplify the search after the origin of the species, I may begin by eliminating the old world, for it is sufficiently evident that the guava came from America. Out of sixty species of the genus Psidium, all those which have been carefully studied are American. It is true that botanists from the sixteenth century have found plants of _Psidium guayava_ (varieties _pomiferum_ and _pyriferum_) more or less wild in the Malay Archipelago and the south of Asia,[1212] but everything tends to show that these were the result of recent naturalization. In each locality a foreign origin was admitted; the only doubt was whether this origin was Asiatic or American. Other considerations justify this idea. The common names in Malay are derived from the American word _guiava_. Ancient Chinese authors do not mention the guava, though Loureiro said a century and a half ago that they were growing wild in Cochin-China. Forster does not mention them among the cultivated plants of the Pacific Isles at the time of Cook’s voyage, which is significant when we consider how easy this plant is to cultivate and its ready dispersion. In Mauritius and the Seychelles there is no doubt of their recent introduction and naturalization.[1213]