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256 PROCEEDINGS OF THE AMERICAN ACADEMY. 
the supposition that these are islands of elevation, the seeds of Huphorbia 
viminea must have reached them in one of two ways: either each of the 
nine islands, where we know the species now to occur, must have received 
its seed directly from the mainland, or, what is much more natural, seed 
must have reached one or more of the islands and from these spread to 
the rest. That the same species should have reached all these islands 
_ presupposes a considerable facility of transportation. But as soon as 
this is granted it is impossible to understand the highly individual de- 
velopment of the forms upon the different islands. For relative or com- 
plete isolation seems necessary to account for the racially divergent floras 
of the islands; and especially for the occurrence of only one form upon 
each island. It would thus appear necessary, in accounting for the 
present distribution, to assume that at one time in the remote past, the 
islands were either united, or at least that the channels which separate 
them were less formidable barriers to seed-transportation than at present, 
so that a general distribution of species could have been effected ; and . 
that subsequently, as the islands separated, or as the channels through 
some change of currents, or other cause, became less easily passed, an 
era of much greater isolation of the floras of the different islands came 
about. The divergence of character of the vegetation would then begin 
at once, and the otherwise unaccountable existence of a single and 
peculiar form upon each island would be readily intelligible. While not 
prepared to make any positive assertion regarding the probable origin of the 
islands, the authors fail to see in the hitherto generally accepted theory 
of elevation any satisfactory explanation for the harmonic yet divergent 
floras of the different members of the group.” 
Finally, for the subsidence theory, it must be admitted that the direct 
geological arguments for the elevation of the islands are not so forcible 
as they at first appear. Thus, as Baur has pointed out, the fact that all 
parts of the islands now visible are volcanic proves little; for if the 
Andes were sunk until only equivalent land areas remained, they t00 
would appear wholly volcanic; and as to the recent elevation of the 
South American coast, that, as I am informed by Professor W. M. Davis. 
is no conclusive proof that areas five hundred miles to the seaward 
have suffered like elevation or, indeed, that they have not been simulta- 
neously subjected to a sort of counter-balancing subsidence. 
Such, in brief, have been the arguments advanced on both sides re 
garding the origin of the Galapagos Islands. During a re-examination 
of the whole vascular flora of the islands, I have sought further light 
upon this question, and now find the peculiar distribution of the plants 
