DERIVATION OF THE FLORA AND FAUNA 363 



a representation of genera and species in the separate islands of a group; — we can under- 

 stand why we find in the Atlantic island Floras of such a graduated series of forms, 

 ascending from variety to genus, without those sharj) lines of specific distinction that 

 continental plants exhibit; — why whole tribes are absent in the Islands; why their Floras 

 are limited, and sj^ecies few in proportion to genera; — why so many j^eculiar genera 

 tend to grotesque or |)i<turesque arborescent forms . .. (p. i i ). 



All this is, perhaps, not so easy to understand as HooKI'.R, impressed by 

 Darw INS theor}', thought. Finally I shall quote the summary of Wallace's General 

 remark on Oceanic Islands [2'jS. 329-330), to bring this chapter to a close: 



They all agree in the total absence of indigenous mammalia and amphibia, while 

 their re])tiles, when they jiossess any, do not exhibit indications of extreme isolation and 

 antiquity [for the moment Wallace seems to have forgotten the giant tortoises and the 

 peculiar endemic lizards in the Galapagos, typically oceanic islands in his opinion]. 

 Their birds and insects j^resent just the amount of specialisation and diversity from con- 

 tinental forms which may be well explained by the known means of dispersal acting 

 through long {)eriods; their land shells indicate greater isolation, owing to their admittedly 

 less effective means of conveyance across the ocean; while their plants show most clearly 

 the effects of those changes of conditions which we have reason to believe have occurred 

 during the Tertiary epoch, and preserve to us in highly specialised and archaic forms 

 some record of the primeval immigration by which islands were originally clothed with 

 vegetation. 



Chapter VIII. 



Evolution in Oceanic islands. 



Ever since the high proportion of endemic organisms in oceanic islands and 

 especially the occurrence of systematically isolated genera were first noticed, an 

 explanation of this condition has been sought. Most authors have, as we have seen, 

 assumed that the islands never had been connected with a continent and that, 

 consequently, their entire living world had developed from a limited number of 

 ancestors carried across the water. Even if the islands had emerged as late as during 

 the Pliocene, the time was thought to have been sufficient for immigrants to get 

 transformed. It was a peculiar island world, the Galapagos Archipelago, which gave 

 birth to Darwin's theory of origin of species through variation and natural selec- 

 tion, and Hooker, when dealing with a number of islands, was convinced that 

 Darwin had given the solution to their problems and that their status strongly 

 supported his theory: 



And if many of the phenomena of oceanic island Flora are thus well explained by 

 aid o^ the theory of the derivative origin of species, and not at all by any other theory, 

 it surely is a strong corroboration of that theory. Depend upon it, the slow but steady 

 struggle for existence is taking advantage of every change of form and every change of 

 circumstance to which plants no less than animals are exposed; and, variation and change 

 ot form are the rules in organic life. . . . By a wise ordinance it is ruled, that amongst 

 the living beings like shall never produce its exact like; as no two circumstances in 

 time or place are absolutely synchronous, or equal, or similar, so shall no two beings 

 be born alike; that a variety in the environing conditions in which the progeny of a living 

 being may be placed, shall be met by variety in the progeny itself. A wise ordinance 



