THE PALAEOTROPICS 177 



very much like the corresponding shores of Africa on the w< 

 side of the Red Sea, to an elevation of about 9,000 feel . 



As in Abyssinia, the higher mountains intercept the moisture- 

 laden winds from the Indian Ocean, and the upper and intermediate 



elevations receive a fairly abundant rainfall, so that a luxuriant 

 vegetation of sub-tropical and warm temperate type flourish* 

 Very little moisture passes inland and the elevated plateau soon 

 merges into the desert which covers much the greater pari of 

 Arabia. The rainfall at the higher elevations is supplemented by 

 frequent clouds and mists, and heavy dews play their part in 

 conserving moisture. Conditions are especially favorable in the 

 deep valleys and gorges eroded by the mountain streams. 



The vegetation of the mountains much resembles that of the 

 Abyssinian highlands, but there is also a large endemic element 

 more nearly allied to true Asiastic species, and related to the desert 

 vegetation to the east. 



Of the indigenous plants, the original coffee (Coffea arabica), 

 is the most notable. The Arabian town of Mocha is inseparably 

 associated with this famous product of Arabia. As we have seen, 

 other species of coffee occur in various parts of Africa, and one of 

 them, the Liberian coffee, is extensively cultivated in regions 

 where the Arabian coffee does not thrive. 



With the sub-tropical vegetation related to the Abyssinian flora, 

 there are a good many Mediterranean species, so that the flora 

 as a whole is an extensive one. This portion of Arabia was formerly 

 much more densely populated than at present, and the centre of 

 an important trade in gums, balsams, spices, etc., which abound in 

 the hot semi-arid regions of medium elevation. 



"Araby the blest," " Arabia felix" of the ancients has sadly 

 declined from those days when it was the source of the prized 

 balsams and spices. The Arabian balsam was the product of 

 trees of two genera Boswellea and Balsamodendron. Species 

 of Acacia, as in Africa, are common, and from some of them the 

 gum-arabic of commerce is derived. 



India 



Only about half of the total area of India lies actually within 

 the tropics, and in the northwestern part, and much of t he Himala- 

 yan districts, sub-tropical rather than tropical conditions prevail. 



