There are powerful arguments in favour of an American origin. The fifteen known species of the genus _Batatas_ are all found in America; eleven in that continent alone, four both in America and the old world, with possibility or probability of transportation. The cultivation of the common sweet potato is widely diffused in America. It dates from a very early epoch. Marcgraff[145] mentions it in Brazil under the name of _jetica_. Humboldt says that the name _camote_ comes from a Mexican word. The word _Batatas_ (whence comes by a mistaken transfer the word potato) is given as American. Sloane and Hughes[146] speak of the sweet potato as of a plant much cultivated, and having several varieties in the West Indies. They do not appear to suspect that it had a foreign origin. Clusius, who was one of the first to mention the sweet potato, says he had eaten some in the south of Spain, where it was supposed to have come from the new world.[147] He quotes the names _Batatas_, _camotes_, _amotes_, _ajes_,[148] which were foreign to the languages of the old world. The date of his book is 1601. Humboldt[149] says that, according to Gomara, Christopher Columbus, when he appeared for the first time before Queen Isabella, offered her various productions from the new world, sweet potatoes among others. Thus, he adds, the cultivation of this plant was already common in Spain from the beginning of the sixteenth century. Oviedo,[150] writing in 1526, had seen the sweet potato freely cultivated by the natives of St. Domingo, and had introduced it himself at Avila, in Spain. Rumphius[151] says positively that, according to the general opinion, sweet potatoes were brought by the Spanish Americans to Manilla and the Moluccas, whence the Portuguese diffused it throughout the Malay Archipelago. He quotes the popular names, which are not Malay, and which indicate an introduction by the Castillians. Lastly, it is certain that the sweet potato was unknown to the Greeks, Romans, and Arabs; that it was not cultivated in Egypt even eighty years ago,[152] a fact which it would be hard to explain if we supposed its origin to be in the old world.