The great continent of Asia, of which Europe, as we have seen, is but a peninsula, can be divided into a series of zones, distinguished alike by climate and by vegetation. To the north we have the cold tundra region, passing to the south into the forest region. The Asiatic forest region is continuous with that of Europe, but while the European forest extends southward till Mediterranean conditions intervene, close to the sea of that name, the Asiatic forest has its southern limit in about the latitude of London. To the south of the Asiatic forest stretches a zone of steppes passing into desert, and even into tundra in the elevated regions of Central Asia. The steppe region, as we have already indicated, enters Europe by way of Russia and pushes a long arm up the Danube into Hungary. South of the Asiatic steppes and deserts comes an interrupted band of warm temperate or tropical forest, luxuriant to the east where there are summer rains, scanty and scrub-like to the west, where Asia meets the Mediterranean. The steppes and desert of Asia are populated, scantily enough, with wandering pastoral nomads, who constantly tend to overflow from their own region into those of the surrounding agricultural populations. These agricultural populations are concentrated in three areas, all specially favoured by nature. To the east the summer rains, the luxuriant indigenous flora, and the presence of great river valleys, that is, of naturally fertile regions, led to the early establishment of agricultural populations in China and India. Further to the west, the fertile valleys of the Tigris and Euphrates early saw the founding of a great civilisation. This region, the Mesopotamia of geographers, is very near the third area, the Mediterranean, though far enough removed to have a very scanty rainfall, which made irrigation a necessity for agriculture. Its inter-relations with the Mediterranean must have begun early, and, remembering that part of the Mediterranean itself is in Asia, we need not stop to discuss the vexed question as to whether the Mediterranean civilisation was largely indigenous, or originated in the continent of Asia. It is often difficult to ascertain whether plants which have long been grown in the Mediterranean area, and are well-fitted to it, are really indigenous there, or were brought to it from the Mesopotamian countries. There is much similarity of climatic conditions, and for our purpose it is sufficient to note that the cultivated plants of the Mediterranean basin fall into three main categories. There are, first, the plants specially adapted to its climate; these are either native or were introduced from the countries close at hand. Second, there are many plants, much less perfectly adapted to conditions of drought, and therefore often demanding irrigation in summer, which were introduced from the Far East, after they had been cultivated there for long periods. Thirdly, and much fewer