296 



ISLAND LIFE. 



[par T II 



paper on the Compositae/ Mr. Bentliam gives us some valuable 

 remarks on the affinities of the seven endemic species belonging 

 to the genera Commidendron, Melanodendron, Petrobium, and 

 Pisiadia, which form so important a portion of the existing 

 flora of St. Helena. He says : " Although nearer to Africa 

 than to any other continent, those composite denizens which 

 bear evidence of the greatest antiquity have their affinities for 

 the most part in South America, while the colonists of a more 

 recent character are South African." . . . ^' Commidendron and 

 Melanodendron are among the woody Asteroid forms exemplified 

 in the Andine Diplostephium, and in the Australian Olearia. 

 Petrobium is one of three genera, remains of a group probably 

 of great antiquity, of which the two others are Podanthus in 

 Chile and Astemma in the Andes. The Pisiadia is an endemic 

 species of a genus otherwise Mascarene or of Eastern Africa, 

 presenting a geographical connection analogous to that of the 

 St. Helena Melhanise,^ with the Mascarene Trochetia." 



Whenever such remote and singular cases of geographical 

 affinity as the above are pointed out, the first impression is 

 to imagine some mode by which a communication between 

 the distant countries implicated might be effected ; and this 

 way of viewing the problem is almost universally adopted, even 

 by naturalists. But if the principles laid down in this work 

 and in my Geoyraj^liical Distribution of Animals are sound, 

 such a course is very unphilosophical. For, on the theory of 

 evolution, nothing can be more certain than that groups now 

 broken up and detached were once continuous, and that frag- 

 mentary groups and isolated forms are but the relics of once 

 widespread types, which have been preserved in a few localities 

 where the physical conditions were especially favourable, or 

 where organic competition was less severe. The true explana- 

 tion of all such remote geographical affinities is, that they date 

 back to a time when the ancestral group of which they are the 

 common descendants had a wider or a different distribution ; 



1 "Notes on the Classification, History, and Geographical Distribution 

 of Composita3."— JoztrmZ of the Linnean Society, Vol. XIII. p. 563 (1873). 



2 The Melhaniee comprise the two finest timber trees of St. Helena, now 

 almost extinct, the redwood and native ebony. 



