252 Dr. J. D. Hooker on the Vegetation 



to the west of the American Cordillera and the Galapagos, or only to cross 

 to the eastward on the lowest part of Mexico. 



Drymaria glaberrima. Verbena littoralis. 



Acacia Cavenia. polystachya. 



Cassia picta. Plantago tomentosa. 



Baccharis pilularis. Cryptocarpus pyriformis. 



Dictyocalyx Miersii. Boussingaultia baselloides. 



Clerodendron molle. Mariscus Mutisii. 



Again, these 120 are of such common occurrence over a large extent of 

 coast, that their introduction into the Galapagos by causes now in operation 

 can hardly be doubted. Presuming that such is the case, it may not be out of 

 place to trace here the course of migration, the means by which it may have been 

 effected, and the facilities for transport presented by the individual species. 



The position of the group between the Pacific Islands and America, points 

 to these as the only mother-countries from which plants could have migrated. 

 We have seen that many are common to the latter country ; but as at least 

 15 species are also found in the South Sea Islands, it may be supposed that 

 there has been migration from that quarter, especially as many plants are 

 dispersed in a very remarkable manner over every group in the Pacific, esta- 

 blishing themselves very soon after the formation of any new land, and whose 

 further extension to the Galapagos might have been deemed possible*. 



There are 16 species found both in the Galapagos and South Sea Islands, 

 which is nearly the half of what are common to the latter locality and 

 America, — a very large proportion ; but as they are unaccompanied by any 



* The species to which I allude as being so very prevalent over the tropical South Sea Islands, 

 are : — 



Oxalis comiculata. Sccevola Koenigii. 



Dodoneea viscosa. Cordia orientalis. 



Lepidium piscidium, Pisonia mitis. 



Tephrosia piscatoria. Achyranthes velutina. 



Guilandina Bonduc. Aleurites triloba. 



Sesuvium portulacastrum. Pandanus odoratissimus. 



Metrosideros polymorpha. Cocos tmcifera. 



Portulaca oleracea. DavalUa solida. 



Adenostemma viscosnm. Phymatodes vulgaris ; 



together with several other Ferns, some Cyperacete and Graminece. 



