418 APPENDIX E. 



In the first place, nearly all the characteristic Canarian 

 types are absent in the eastern group. Out of fifty-four genera 

 above enumerated as present in the Canaries but wanting in 

 Marocco, two are in the Canaries confined to the eastern 

 islands : one of these, Traganum, is an African desert type, 

 probably to be found in South Marocco ; the other, Melianthus, 

 a Southern African plant, and scarcely indigenous. Of the re- 

 mainder Plocama alone is certainly present, and three other 

 generic types probably exist in that group ; while forty-eight 

 genera, including eight out of nine peculiar to the Canaries, are 

 apparently absent. In the next place several characteristic 

 desert plants, such as Oligomeris subulata, Ononis vaginalis, 

 Convolvulus Hystrix, and Traganum nudatum, are present in 

 the ' Purpurarise,' but absent from the western islands. 



Although the Flora of the Purpurarise is incompletely known, 

 and our acquaintance with that of the neighbouring African 

 coast between the rivers Sous and Draha is extremely imperfect, 

 these facts tend to prove that there is a closer botanical rela- 

 tionship between the eastern islands and the adjoining continent 

 than there is between them and the western portion of the 

 Canarian Archipelago. Such relationship might be brought 

 about in three difierent ways. 



1. The greater dryness and heat of the eastern islands may 

 have favoured the immigration of African forms, and at the 

 same time led to the destruction, or weeding out, of the cha- 

 racteristic Canarian types. In this case the cause would be of 

 a purely local and climatic character. 



2. We may believe in the trans-oceanic migration of some 

 African species to the nearer islands, along with the transport of 

 some Canarian species (those enumerated in p. 416, and others 

 which may be hereafter found) to the neighbouring continent. 



3. An ancient extension of the continent to the Purpurarise, 

 leaving the other islands separated by deep sea. 



It is an objection to the latter hypothesis that a profoundly 

 deep ocean bed lies between the lines of 100 fathom soundings 

 that gii-dle the islands and the African coast respectively ; and 

 that while the 100 fathom line extends about thirty miles from 

 the coast of the continent, it is never more than five miles, 

 rarely more than one or two, from those of the islands. 



In favour of the hypothesis of trans-oceanic transport it may 

 be remarked that the distance between the African coast and 



