_Dioscorea japonica_, Thunberg, cultivated in Japan, has also been found in clearings in various localities, but Franchet and Savatier[302] say that it is not positively known to what degree it is wild or has strayed from cultivation. Another species, more often cultivated in Japan, grows here and there in the country according to the same authors. They assign it to _Dioscorea sativa_ of Linnæus; but it is known that the famous Swede had confounded several Asiatic and American species under that name, which must either be abandoned or restricted to one of the species of the Indian Archipelago. If we choose the latter course, the true _D. sativa_ would be the plant cultivated in Ceylon with which Linnæus was acquainted, and which Thwaites calls the _D. sativa_ of Linnæus. Various authors admitted the identity of the Ceylon plant with others cultivated on the Malabar coast, in Sumatra, Java, the Philippine Isles, etc. Blume[303] asserts that _D. sativa_, L., to which he attributes pl. 51 in Rheede’s _Hortus Malabaricus_, vol. viii., grows in damp places in the mountains of Java and of Malabar. In order to put faith in these assertions, it would be necessary to have carefully studied the question of species from authentic specimens. The yam, which is most commonly cultivated in the Pacific Isles under the name _ubi_, is the _Dioscorea alata_ of Linnæus. The authors of the seventeenth and eighteenth centuries speak of it as widely spread in Tahiti, in New Guinea, in the Moluccas, etc.[304] It is divided into several varieties, according to the shape of the rhizome. No one pretends to have found this species in a wild state, but the flora of the islands whence it probably came, in particular that of Celebes and of New Guinea, is as yet little known. Passing to America, we find there also several species of this genus growing wild, in Brazil and Guiana, for instance, but it seems more probable that the cultivated varieties were introduced. Authors indicate but few cultivated species or varieties (Plumier one, Sloane two) and few common names. The most widely spread is _yam_, _igname_, or _inhame_, which is of African origin, according to Hughes, and so also is the plant cultivated in his time in Barbados.[305]