But the supply could not keep up with the insatiable demand. The great expeditions which were organized to sweep the Terra Firma and the adjacent islands of their population found the warlike Caribs difficult to procure.[4] The supply of laborers was failing just at the period when the colonists began to see that the gold of Hayti was scattered broadcast through her fertile soil, which became transmuted into crops at the touch of the spade and hoe. Plantations of cacao, ginger, cotton, indigo, and tobacco were established; and in 1506 the sugar-cane, which was not indigenous, as some have affirmed, was introduced from the Canaries. Vellosa, a physician in the town of San Domingo, was the first to cultivate it on a large scale, and to express the juice by means of the cylinder-mill, which he invented.[5] The Government, seeing the advantages to be derived from this single article, offered to lend five hundred gold piastres to every colonist who would fit up a sugar-plantation. Thus stimulated, the cultivation of the cane throve so, that as early as 1518 the island possessed forty sugar-works with mills worked by horse-power or water. But the plantations were less merciful to the Indians than the mines, and in 1503 there began to be a scarcity of human labor. At this date we first hear that negroes had been introduced into the colony. But their introduction into Spain and Europe took place early in the fifteenth century. "Ortiz de Zunigo, as Humboldt reports, with his usual exactness, says distinctly that 'blacks had been already brought to Seville in the reign of Henry III of Castile,' consequently before 1406. 'The Catalans and the Normans frequented the western coast of Africa as far as the Tropic of Cancer at least forty-five years before the epoch at which Don Henry the Navigator commenced his series of discoveries beyond Cape Nun.'"[6]