466 SCIENCE PROGRESS. 



desert regions of the mainland, consisting largely of dwarf, 

 stunted, densely-branched, often spiny and hairy shrubs. 

 The hill-slopes and valleys present a much more vigorous 

 and luxuriant growth, composed of representatives of 

 genera characteristic of the tropics of the Old World ; but 

 the arboreous element is limited to trees of small stature, 

 from twenty to twenty-five feet high. It is so dense, how- 

 ever, as to be almost impenetrable in places. " Once out 

 of the valley and upon the plateaux, the scene is quite 

 different. Wide barren stretches of grey limestone, or 

 undulating prairie-like downs, extend on every side, un- 

 relieved, save by an isolated Draccena or tree-euphorbia of 

 stiff erect habit, looking" like the remnant of the vegetation 

 of some old geological epoch, or where a lake-like de- 

 pression, with its brown earth sparingly coated with green 

 herbage, often of rank luxuriance, intervenes. And when 

 we reach the higher altitudes on the granitic range, the 

 vegetation at once impresses one with its sub-temperate 

 character. The arborescent type has almost entirely dis- 

 appeared. Shrubby composites, such as species of Psiadia, 

 Pluchea and Euryops, and succulent forms of Senecio are 

 found, also crowds of Helickrysum, many of them strongly 

 aromatic, and scenting the air under the stimulating sun- 

 rays ; and quaint types such as Thamnosma, Nirarathamnos, 

 Graderia, Ccphalocroton, Coccuhis Balfonrii, and others, 

 are frequent. Twiggy, narrow-leaved herbs form a dense, 

 deep carpet on the soil, interrupted here and there by a 

 protruding lichen-covered boulder, and for all the world 

 like the covering of heather on a northern moor ; whilst 

 within the shade of the boulders, or in the moisture of the 

 overhanging cliffs in the ravines, bright green herbs, such 

 as Galium and Gypsophila, nestle in beds of liverwort and 

 moss." 



It is in the middle and upper zone of vegetation that a 

 large proportion of the singular endemic types exist. A 

 few of the more specially interesting and curious vegetable 

 inhabitants of Socotra deserve brief mention. Cocculus 

 Balfonrii (Menispermaceae) is an erect densely branched, 

 rigid shrub, developing both broad cladodes and leafy 



