THE CANARIAN FLOEA. 417 



Canarian Flora, there are some of them whicli so intimately 

 bear upon the Maroccan as to awaken attention. 



The wonderful development in the Canaries of endemic 

 species belonging for the most part to Mediterranean types, points 

 to the very early introduction of the parent forms of these, and 

 the long isolation both of the Archipelago and its separate islets. 

 It is in accordance with generally accepted views, to assume that 

 the endemic species of each genus have been derived from parent 

 forms originally introduced into one or more of the islets ; and 

 that as the descendants of these species spread over the Archi- 

 pelago they were exposed to different conditions in each islet, re- 

 sulting in their varying, and in the segregation and conservation 

 of different local varieties each in its own insular birth-place ; a 

 supposition which is in accordance with the fact that those 

 endemic species are really very local, many being confined to a 

 single islet. In Marocco the parent forms of its Flora would 

 be exposed to no such diverse conditions, and the areas in 

 which varieties occu.rred, not being isolated, would be exposed 

 both to invasion on all sides by other jjlants, and to destruc- 

 tion by agencies that affected the whole surrounding country, as 

 drought, floods, insects, and birds. 



The tropical types in the Canaries, with the exception of 

 the Egypto- Arabian and the trees mentioned under V. c, 

 are chiefly weeds of wide distribution, which have not reached 

 Marocco, because of its want of ports and its limited commerce. 

 Finally the Draccetia, together with the tropical trees of 

 MyrsinecB, Sapotacece (in Madeira), and Laurinece, and the 

 Egypto- Arabian types, suggest the hypothesis that at a very re- 

 mote period these and many other plants of warmer and damper 

 regions flourished in the area included in North- West Africa and 

 its adjacent islands, and that they have been expelled from the 

 continent by altered conditions of climate, but have been pre- 

 served in the more equable climate and more protected area of 

 the Atlantic Islands. 



Ball, who has given me valuable aid on many points dis. 

 cussed in this article, directs my attention to the important 

 differences that exist between the vegetation of the eastern 

 group of the Canary Islands — Fuertaventura, Lanzarote, and 

 the adjacent islets — the ' Purpurarise ' of authors, and the west- 

 ern group, including Teneriffe, Grand Canary, ifec. 



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