240 PROCEEDINGS OF THE AMERICAN ACADEMY. 



for the introduced species are for the most part the pUints of the "West 

 Indian Islands and of the lower hot parts of the South American coast, 

 whilst the peculiar Flora is chiefly made up of species not allied to 

 the introduced, but to the vegetation which occurs in the Cordillera or 

 the extra-trojjical parts of America." But, after rejjeated efforts, I am 

 unable to verify this double relationship, and must infer that subsequent 

 discoveries, both upon the mainland and upon the islands, have done much 

 to weaken the grounds upon which these conclusions once rested. Many 

 cases could now be cited to show that the endemic plants of the Gala- 

 pagos Islands, far from forming a marked or peculiar class, are often the 

 nearest allies of species or varieties which are common to the islands and 

 the continent. Both classes include alike the most widely diverse ele- 

 ments, —xerophy tic, mesophytic, and halophytic types, annuals and peren- 

 nials, herbs, shrubs, and trees, climbers and epiphytes, — and both occur m 

 common at all altitudes and in every sort of habitat the islands afford. 

 Accordingly it is not remarkable to find their closest congeners occupying 

 the same diverse habitats upon the mainland from the hot, moist lowlands 

 about Guayaquil and Panama to the cool parts of the Andes, dry regions 

 of Peru or western Mexico, and in a few instances the more fertile up- 

 lands, of Colombia, Central America, and Mexico. Moreover, the 

 endemic forms show all grades of differentiation from their continental 

 allies ; some are well marked specific types, others mere varieties, while 

 still others are scarcely distinguishable forms. 



It appears, therefore, that very diverse floral elements have reached 

 the archipelago, probably at different times and from widely different 

 habitats. Presumably all have been subjected on the islands to influences 

 of a kind to bring about change in their nature ; and in two-fifths of the 

 plants now known on the islands more or less pronounced evidences of 

 such change can be observed. These plants, which show modification, 

 form, as we have seen, no sharply marked class, but pass over very imper- 

 ceptibly into nearly related forms which it is impossible to differentiate 

 from plants of the mainland. That some plants have reached the Gala- 

 pagos from the West Indian Islands during the subsidence of the Isthmus 

 of Panama is by no means impossible, but as we should expect, these 

 plants, if such there were, have established themselves in like manner 

 upon the western coast and slopes of the continent, so that it is now 

 quite impossible to trace any direct floral affinity between the West 

 Indies and the Galapagos which the latter do not exhibit even in a higher 

 degree with the western parts of the mainland. 



Mr. Hemsley has already commented upon the wide divergence be- 



