lUnTEAX SOCIETT OF LO>T)OIf. xlv 



climate acting more upon plants than upon animals. But there 

 are other circumstances which may probably have favoured the 

 continued action of natural selection through countless ages in 

 procuring this result. Dr. Hooker has very plausibly suggested a 

 greater geological antiquity in the plant races than in those of 

 animals, especially the higher animals, under which the former, or 

 the ancestors from which they are descended, had become established 

 over a wide extent of continuous land before its disruption by suc- 

 cessive upheavals and depressions had produced the present isolation. 

 We must next take into account that this continuity of land need 

 not be so great in the case of plants as of animals. The dispersion 

 of the former is passive, and takes place chiefly in a dormant state, 

 in which minuteness and enormous multiplication affords them 

 opportunities for crossing seas and other barriers denied to the 

 higher animals. Plant-races of accommodating (accomodations- 

 fahiger) constitutions, as they successively arose and attained the 

 full vigour of specific life, will have early spread over any continuous 

 or but little broken area enjoying comparatively similar physical 

 and climatological conditions, the western and eastern forms inter- 

 mingling so as that the one should only gradually be replaced by 

 the other — thus iu early ages repeating under the tropics the pheno- 

 menon now observed in the northern temperate Europaeo-Asiatic 

 region. These vigorous or accommodating races, whether new dif- 

 ferentiations or foreign invasions, will at the same time have gra- 

 dually expelled and replaced races which in tertiary or other previous 

 periods had occupied the land under different conditions, and which 

 now could only maintain themselves in the struggle for life in 

 localities affording them in their reduced or weakened state special 

 protection against the effects of the altered climate and the attacks 

 of their vigorous competitors. Such localities, suited to ancient or 

 expiring races of few individuals with varied but always special 

 requirements, and generally slow of propagation, may be exemplified 

 in the Mediterranean, the Japanese, and other regions abounding, as 

 Grisebach terms it, in centres of vegetation ; they may be faintly 

 traced in the Nilgherries and in Ceylon, but are in general very few 

 in Grisebach 's Monsoon region ; and those few are as yet but little 

 known or wholly unvisited. Kini-Balu, in Borneo, however, has, as 

 we learn from Dr. Hooker, supplied a place of refuge for a certain 

 number of Australian types ; and it maj' be conjectured that many 

 more may have maintained themselves in those lofty mountains of 

 New Guinea which have as yet been only seen from a distance. 

 Continuity of vegetation probably existed in tertiary times between 



