The great accessions of geographical knowledge made during the fifteenth and sixteenth centuries were slow to affect horticulture. Ships were then few and small, and the passage from Hispaniola or Calicut to Cadiz or Lisbon occupied weeks or even months. Moreover, the conquests of Spain and Portugal (Goa, the Moluccas, Brazil, the West Indies, Peru, and Mexico) lay mostly within the tropics, and could furnish hardly any plants capable of enduring a European winter. Special pains were, however, taken to bring over some valuable food-plants which were thought likely to thrive in Europe. Before any European landed in America the potato had been cultivated by the Indians of Peru, a country which, though lying almost under the line, rises into cool mountain-districts. Potato-tubers were soon introduced to Spain and Italy, and a little later to other parts of Europe; Raleigh's planting of potatoes on his estate near Cork came a few years later. The edible tomato, which is distinguished from the wild form by its enlarged fruits, was apparently cultivated in Peru before the first landing of the Spaniards. The unusually high proportion of edible plants among the first importations from America and other distant countries is worthy of remark. Early explorers eagerly sought for valuable food-plants, but the number of such as could be cultivated alive in Europe was very limited, and since the sixteenth century the attention of collectors has been fixed upon ornamental species simply because of the dearth of others. European flower-gardens were enriched during the sixteenth century by the following American species: the so-called French and African marigolds (both from Mexico), sunflowers, the arbor-vitæ (Thuja occidentalis), Yucca gloriosa, and the Agave, misnamed the American Aloe. About the same time the horse-chestnut, lilac, and syringa, or mock-orange, were first brought to central and western Europe, and with them the tulip, richest and most varied of flowering bulbs. All these reached Vienna from Constantinople, but how and when they were brought to Constantinople, or what were their native countries, are still doubtful questions. The horse-chestnut is believed to be a native of Greece, where it is said to grow wild among the mountains; probably it extends into temperate Asia as well. It is said to have reached Constantinople in 1557. Longstanding tradition derives the lilac from Persia, but botanists say that it is also indigenous to parts of south-eastern Europe. The garden-tulip is believed to be native to temperate Asia and also to Thrace; it is, of course specifically distinct from the wild tulip of northern Europe.