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. 

 The 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. 

 For, to quote from a discussion of the forms of Euphorbia viminea, : x 

 " 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 Keen 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 



i Rob. & Greenm. (1), 136. 



