296 
ISLAND LIFE. 
[par T II 
paper on the Composite , 1 Mr. Bentham 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.” . . . u 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 Afiica, 
presenting a geographical connection analogous to that of the 
St. Helena Melhanise , 2 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 Geographical 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 Compositse .” — Journal of the Linnean Society , Vol. XIII. p. 563 (1873). 
2 The Melhaniae comprise the two finest timber trees of St. Helena, now 
almost extinct, the redwood and native ebony. 
