I EET” 
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FLORA OF THE GALAPAGOS ISLANDS. 255 
these islands several different forms of Euphorbia viminea, several very 
nearly related species of Acalypha, many habitally uniform species of 
Borreria, and of many other genera. In many instances these forms are 
confined to a single island, and in the majority of cases each form is more 
closely related to those of the other islands than to any continental ally. 
he same is true of the fauna, for the animals of particular groups, while 
exhibiting near affinity, show slight differences, which can in many cases 
be correlated with their occurrence upon different islands. Thus the 
flora and fauna of the islands are, to use Dr. Baur’s expression, harmonic. 
From this peculiar distribution, which seemed to him wholly inexplic- 
able upon the emergence theory, Dr. Baur advanced the view that the 
Galapagos were islands of subsidence, once attached to the continent by 
some isthmian connection extending presumably to the Central American 
coast. In an enthusiastic presentation of this theory, Dr, Baur certainly 
advanced in support of it some as yet unanswered biological arguments. 
Thus, it explains perfectly the harmonic relations of the living forms upon 
the different islands; for if the islands were once united and then by sub- 
sidence separated, the remnants of their common flora and fauna, persist- 
ing upon the different islands, would have diverged not only from the 
continental types, but from each other. From the depth of ocean between 
the archipelago and the mainland, it would naturally be inferred that the 
islands were cut off from the continent before they were divided from 
each other. This, on the supposition of a gradual variation, would account 
not only for the divergence, for instance, of the genus Scalesia from its 
Mexican allies, but for the minor differences which are found between 
the different species of Scalesia on the several islands, where they occur ; 
While, as we have seen, this harmonic distribution of very similar yet 
slightly differing forms on the different islands has appeared unaccount- 
able, on the theory that these are islands of emergence casually seeded. 
or, to quote from a discussion of the forms of Zuphorbia viminea :* 
“The question at once presents itself, if this archipelago is composed of 
islands of elevation, built up from the sea-floor independently by volcanic 
action, how has such a distribution been effected. If the vegetation has 
been derived from the mainland by the chance transportation of seeds, it 
is quite impossible to believe that each island has received a slightly 
different form of the same species, and we are forced to the much more 
natural assumption that racial and varietal divergence has come about 
after the introduction of the species upon the islands. Now, continuing 
Por Wane Ee Cs PE: A ea 
1 Rob. & Greenm. (1), 136. 
