As a result of their isolation, the proportion of endemic plants is greater here than in any other region, and the great elevation of the mountains, with the consequent variation in temperature, moisture and barometric pressure, has multiplied the number of species.
Most notable of all, yellow fever was eradicated where it had been endemic for centuries.
There are 67 species of birds known from Sokotra, of which 15 are endemic; of 22 reptiles, 3 genera and 14 species are peculiar; and of the land and fresh-water shells, to whose distribution great importance attaches, 44 species out of 47 are confined to the island.
On the other hand, it is rich in Cornpositae, especially Solidago and A ster, Polemoniaceae, Asciepiadaceae, Hydrophyllaceae and Cyperaceae, and it has the endemic Sarracenia, type of a family structurally allied to poppies, of which of the remaining genera Darlingtonia is Californian, and Heliamphora Venezuelan.
Of species common to the two, Maximowicz finds that Manchuria possesses 40% and scarcely 9% that are endemic. Of a collection of about 500 species made in that country by Sir Henry James nearly a third are British.