The second group, that comprising plants introduced from the Far East, includes many valuable fruit trees, which in the region of the absolutely rainless summer mostly require irrigation. The peach came from China in the time of Alexander the Great; the various citrus fruits, lemon, orange, lime, citron, etc., now so characteristic a feature, were introduced from China or India. India also gave rice, extensively cultivated during long ages, and still extensively consumed, though the facility with which communication with the East is now effected makes it relatively little grown, except in the plain of Lombardy, which is easily irrigated. China sent the white mulberry, and with it the cultivation of the silkworm, so important in many regions. From the Far East also came the sugar-cane, very important till the recent development of the sugar beet industry. Cotton also was probably introduced from the Far East, which thus supplied many cultivated plants and has enormously enriched life for Mediterranean man. Of the American plants of late introduction the most interesting is maize, which fed the somewhat limited indigenous civilisation of North America. Maize requires a warm climate with much sunshine, but needs much moisture during its short growing season. It is not a very valuable cereal, but it is enormously productive and therefore cheap. Generally it may be said to be used as food by man only when necessity compels its use. It is thus employed by subject races, _e. g._ negroes, and by the poor in the warmer parts of Europe. In the Mediterranean it is not sufficiently valuable to be grown on irrigated land, and it will not grow without irrigation where the summer is rainless. Where there are summer rains, however, as in North Italy, or where mountain slopes increase the rainfall, as in parts of Greece, or where the land is rendered valueless for wheat by winter flooding, there maize is grown. Generally it occurs within the Mediterranean area wherever the necessary water occurs naturally or can be supplied cheaply. It forms a very important part of the food of the poor in North Italy, for example, but not in the south, where water is too costly. Two other important plants of American origin are tobacco and the potato. The latter plant is little grown in the Mediterranean, but a considerable amount of tobacco is produced. Another American plant, the prickly pear, besides furnishing an edible fruit, is important as a hedge plant within the area.