388 SCIENCE PROGRESS. 



tinguishes three zones, or regions, as he denominates them ; 

 namely, the coast, cloud, and uppermost regions. The 

 coast region includes the " barrancas " or ravines, and the 

 whole of the cultivated part of the country ranging from the 

 sea-shore up to an elevation of about 3000 feet, and conse- 

 quently, it is here, too, that the colonised plants are found. 

 Contrary to what has happened in St. Helena and many 

 other islands, introduced plants have made comparatively 

 little way in the Canaries, and, indeed, in the Azores and the 

 Cape Verd Islands — that is to say, beyond the coast region. 

 It is true that the formerly extensively cultivated cochineal 

 cactus (Opuntia) has over-run the subtropical part of the 

 country ; but what was formerly the chief source of income 

 now remains as a scourge ; being one of the few plants 

 capable of competing with the indigenous vegetation. The 

 endemic palm, Phoenix canariensis, the aloe, the dragon's 

 blood tree, and the cactus-like shrubby and arboreous 

 euphorbias are conspicuous features in the landscape. 

 Tamarix canariensis is the prominent shrub or small tree of 

 the sandy sea-shore ; but the endemic Plocama pendula, a 

 Rubiacea, with the habit of a casuarina, and various cactus- 

 like species oi Euphorbia, are the most striking and character- 

 istic of the inhabitants of the succeeding rocky country. The 

 " Cardon," Euphorbia canariensis forms dense clumps live 

 or six feet high, consisting of numerous thick, fleshy, angular, 

 prickly stems springing from the same root. But the com- 

 monest and tallest of this genus is the "Tabayba," Euphorbia 

 Regis JttbcE, occupying the driest situations in the Western 

 Canaries, sometimes growing to a height of twenty-five feet, 

 and forming densely-branched hemispherical masses. In- 

 dependently of the paragraphs in the essay cited, Dr. Christ 

 has a special article on the Canary species of Euphorbia 

 (29). The famous " Dragon's Blood Tree ' : {Draccena 

 Draco) is, or rather was, an even more striking feature in 

 the endemic vegetation of the barrancas. 



With regard to the great age formerly attributed to this 

 colossal monocotyledonous tree (Draccena Draco), Dr. 

 Christ's measurements confirm the opinion expressed by the 

 writer (30). There is no doubt now that it is of exceed- 

 ingly rapid growth. A trunk of one growing at I cod los 



