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. South Siberian, Dahurian, Mantchurian, and Japanese plants, which attain their southern limit in Hongkong.

The number of Hongkong species which I would attribute to each of these Floras is given in the following Table. It mast be remembered, however, that these are approximative only, the limits of the areas of species are so vague, their extent so diversified, scarcely two species being ever precisely similar in this respect, that it would be impossible to class them with precision, even were their area always perfectly well known to us.

Let these be compared with the Floras of two districts similarly circumstanced as to maritime position and proximity to the mainland, nearly the same in size and elevation above the sea, but widely different as to soil and climate, viz.:—

1. Aden Peninsula, off the coast of Arabia, in lat. 12° 47′. A dry, parched, volcanic, rocky peninsula or almost an island, about 5 miles long by 3 in breadth, the highest peak attaining 1775 ft., and connected with the mainland by a narrow sandy isthmus. It is exposed throughout the year to a scorching sun, occasionally deprived of rain for a year and a half, and never receives an annual fall of above 6 or 7 inches. Winds are not frequent and seldom violent.

2. Ischia Island, off the Neapolitan coast, in lat. 40° 41′. A volcanic rocky mountain mass, nearly 6 miles long by 3½ in breadth, the highest peak attaining 2,407 ft., and about 9 miles distant from the mainland. Hot and dry during the summer months, it is however well refreshed by rains during the remainder of the year. The thermometer very rarely