North-west India ... 21 



Persia 19 



Senegal 19 



Mediterranean 18 



FLOETJLA ADEKENSIS. XI 



distribution, fourteen occurring over all the barren parts of the 

 •'lobe. The following Table shows how they spread east and west 

 from Arabia as their centre : — 



Table of Distribution of Aden Plants. 



Species. 



Arabia 68 



Scinde 44 



Egypt 29 



Abyssinia 25 



The desert flora, of which these species form a part, attains its 

 greatest breadth in the African desert, about 5° east longitude, 

 where it covers the territory between the 10th and 37th degrees 

 of north latitude. In Asia, though prolonged into Scinde and the 

 western portion of the Punjab, it is diminished in breadth to 

 7° or 8° of latitude ; its southern limit being 23° north latitude in 

 Scinde, and 30° or 31° north latitude in Affghanistan and the Pun- 

 jab. The limits of this vegetation may be defined as follows : — 

 Starting from its head- quarters, the rainless region of Arabia, the 

 flora extends over the peninsula of Arabia, with the exception of 

 the south-western mountainous district, and along the shores of 

 the Persian Gulf, whence it spreads into Southern Persia. It in- 

 cludes the whole of Beloochistan, South Affghanistan, Scinde, and 

 a part of the Punjab. West from Arabia Petraea the flora passes 

 into Egypt and Nubia, and partially into Abyssinia, and extends 

 over the African desert to Senegal ; finding its western limit in 

 the Cape de Verd Islands. Even there it retains many of its most 

 desert types, as is shown by the flora of these islands containing 

 twenty-nine genera common also to Aden and other parts of 

 Arabia, and eleven species absolutely identical : a resemblance the 

 more remarkable from the small number of species composing the 

 Cape de Verd Flora. Webb, in the ' Spicilegia Gorgonica,' enu- 

 merates only 235 species of flowering plants, of which the follow- 

 ing genera are represented at Aden. Those plants of which the 

 specific name is given are identical in both floras. 



Polygala triflora, Linn. Indigofera. 



Mollugo. Rhynchosia. 



Abutilon. Cassia. 



Corchorus Antichorus, Roem. Acacia. 



Grewia. Citrullus colocynthis, Schrad. 



Fagonia cretica, Linn. Oldenlandia. 



Zygophyllum simplex, Linn. Vernonia. 



Zizyphus. Heliotropium. 



