1883.] on the Island of Socotra and its Recent Bevelations. 311 



weeds of cultivation. A large proportion, about l-3rd, are species 

 belonging to Tropical Africa and Tropical Asia. The greater 

 number of these are limited to the plain region of North-East 

 Africa, and South- West Asia, reaching as far as Scindh and 

 Afghanistan, and there forming part of the great desert flora. But a 

 few extend into the Indian Peninsula itself, even reach the Malay- 

 Archipelago, or spread into Australia (the latter form about l-13th of 

 the whole third). Westwards we find an extension of a considerable 

 proportion of this third (about l-8th), passing to the Mediterranean 

 region and the Canary Islands, whilst some (about l-6th) reach the 

 Cape de Verde Islands. Of the remainder of the non-endemic flora, 

 a fair proportion (about 1-1 6th) are found in Tropical Africa alone, 

 chiefly in Abyssinia, and a smaller j)roj)ortion (about l-20th) are 

 natives of Asia, chiefly Arabia, but are not African. A few are re- 

 stricted to South Africa, a few are Indian alone, one is Mascarene 

 and Indian, and one is Gorgonian. 



In the endemic flora we find many plants of very antiquated 

 types. These occur especially on the hill regions of Haghier. Such 

 are Draccena, tree Euphorhia, Euryops, Aloe, Thamnosma, Cocculus, 

 Dendrosicyos, &c. We find also a fair number of genera whose 

 maximum development takes place in temperate regions. Of the 

 genera comprising this flora about 2-5ths have a wide troj)ical range, a 

 fair number are common to Tropical Africa and Asia, and a few are 

 chiefly Mediterranean. Amongst those having restricted distribution 

 may be noted three, Diceratella, Taverniera and Anisofes, which are 

 small genera of the plains of South- West Asia. Caminjlantlms, 

 represented at Aden, has a single species in the Cape de Verde 

 Islands. Three genera are essentially Tropical African — Cephalo- 

 croton, Eureiandra, and Camptoloma, and of these the last two are 

 ditypic and found only in Angola. Graderia and Bahiana are genera 

 not found beyond the limits of South Africa ; whilst Lasiocarys is a 

 South African genus having a single rtpresentative in Abyssinia, and 

 Euryops is a South African one, with one species in Arabia. 



The only purely Indian genus is the ditypic Priofropis. 



The occurrence in Indian Ocean islands of restricted New World 

 types or of forms related to these is a remarkable and well-known fact 

 of distribution. We have for examj)le the Sapotaceous Labourdonnaisia 

 represented in Natal, Mascarene Islands, and Cuba ; the Lauriueous 

 Ocotea with representatives in Canary Islands, South Africa, and 

 Madagascar, its main distribution being American ; and the Eodri- 

 guesian Matlmrina with its nearest ally the Central American 

 Erhlicliia. In Socotra we have illustrations of the same peculiarity. 

 The Eutaceous genus Thamnosma is otherwise represented in Cali- 

 fornia by one species and in Texas by another, and its occurrence is 

 the more remarkable as with the exception of Peganum it is the only 

 genus of true Eues found in the New World. Amongst the endemic 

 genera we have a like feature, for the Verbenaceous Codocarpum is 

 almost congeneric with the tropical and sub-tropical American 



b 



