220 University of California Puhlications in Botany [Vol. 6 



Secondly, though far behind, comes the factor of geographical posi- 

 tion. Islands in proximity have more species in common than those 

 that are far apart — at least in most cases, and to some degree. 



Thirdly, there appears to be a slightly greater influence of the 

 southeastern than of the western and central groups upon most of the 

 smaller islands. This may be due to the southeastern islands being 

 nearer the continent, or being the first to be washed by the flow of 

 the Humboldt current, or lying to the windward of the others. At 

 best, however, this southeastern preponderance is little more than 

 nominal. 



As regards the origin of the islands — a question which is primarily 

 a geological one, though of interest to the biologist because its answer 

 will enable him better to trace the processes of evolution of animal 

 and plant life — Professor Robinson inclines rather to the emergence 

 theory, Dr. Stewart favors that of subsidence, and I do not believe 

 that a satisfactory answer can be given on botanical grounds, at least 

 not without some new method of attack. If the islands arose from 

 the ocean, and were gradually stocked with plants, different species 

 would be bound to reach the individual islands at various times ; biit 

 some, at least, of these would again be commimicated to other islands. 

 On the other hand, if the archipelago should be the remnant of a 

 larger sunken block of land, there would no doubt have been greater 

 original uniformity of distribution ; but with the lapse of time there 

 would be increasing diversity due to the formation of local varieties 

 as well as the dying out in certain islands of species originally occur- 

 ring there ; while on the other hand the factor of dispersal and trans- 

 mission of species from island to island would be operating simultane- 

 ously. It thus seems impossible to decide from a mere knowledge that 

 such and such species are or are not now common to such and such 

 islands, how far each of these various and conflicting processes has 

 been at work. 



The origin of the Galapagos Islands, then, is scarcely a soluble 

 botanical problem. As regards the internal floral relationships of the 

 archipelago, it appears that there is little that is not explainable on 

 the basis of mathematical chance operating evenly as if all the islands 

 ■formed a unit ; with this factor disturbed in some measure by ordinary 

 geographical influences. 



Transmitted November 2, 1914. 



