FLOBULA ADENENSIS. Vll 



temperature of the soil at 107° Fahr. a few feet below the sur- 

 face. In the hotter seasons of the year, the sun, even in the early 

 morning, is overpowering, and above the rocks the air flickers 

 from the intense heat ; while all distant objects are distorted by an 

 imperfect mirage. Almost perpetual drought is, of necessity, the 

 concomitant of such a climate as I have described, and accordingly 

 the annual rain-fall at Aden never exceeds G or 7 inches ; this 

 scanty amount being spread over the period between October and 

 the end of April ; while occasionally none falls for a year and a 

 half. Still Aden is not considered unhealthy, even to Europeans, 

 who seem to become soon accustomed to the heat ; and so great is 

 our power of adaptation to circumstances, that after a residence 

 of a year or two the climate is spoken of as cool and pleasant from 

 October to the end of March, and as bearable during the remain- 

 der of the year. 



2. The vegetation of Aden closely resembles that of Arabia 

 Petraea, of which it is evidently the southern extension. It is 

 eminently of a desert character ; the species being few in number 

 (only 9-4), and being quite disproportioned to the number of 

 genera and Natural Orders ; even when the flora is compared 

 with those of localities having similar areas, and similar rela- 

 tions to the mainland. Most of the species are limited in the 

 number of individuals, a few only of the more arid forms pre- 

 dominating. Dipterygium glaucum, six or seven species of Cap- 

 paridacece, Reseda amblyocarpa, Cassia pubescens and obovata, 

 Acacia eburnea and a few EupJiorbiacece are the only common 

 plants ; and some of these are so plentiful, that in many places 

 they abound to the exclusion of all other plants. The other 

 species are either very local, or sparingly scattered over the 

 peninsula. 



All the species are more or less peculiar in their habit, and 

 some are so strange in their appearance as to constitute the ano- 

 malies of the Natural Orders to which they belong. As examples 

 may be enumerated :— Spluerocoma Hookeri among Caryophyllacea; 

 Adenium obesum, with its almost globular fleshy trunk, naked 

 branchlets bearing a tuft of leaves and an umbel of beautiful 

 flowers, Moringa aptera, in which the leaves are reduced to long 

 subrigid raches, the prickly Jatropha spinosa, and, strangest of all. 

 the uEluropus Arabicus, a grass with short spiny leaves, so sharp, 

 that it was with the greatest difficulty I could procure specimens 

 of it. The bright-green colour, which forms so pleasing a feature 

 of the vegetation of the temperate and moist tropical regions of 



