246 Dr. J. D. Hooker on the Vegetation 



features in common with the similarly barren island of Ascension, where 

 almost the only Dicotyledonous plants are one of Rubiacece and a prostrate 

 Euphorbia, allied to, and of the same habit as, the Gaiapageian ones. The 

 Aristida too of Ascension, which is there the only abundant grass, is repre- 

 sented here by two congeners which occupy similar situations, lliis feeble 

 though decided analogy existing between the vegetation of arid volcanic islets 

 in opposite oceans is very singular, and is a feature analogically repeated as 

 it were by the two moister islands of Juan Fernandez and St. Helena, which 

 possess very similar and closely-allied peculiar forms of fVahlenbergia. 



The shrubby Crotons of this group are no doubt conspicuous features in 

 the vegetation ; the other species of the order are mere weeds. 



RuBiACE^. — An order largely represented, including upwards of ^^5^ of the 

 flowering plants, whilst of the tropical Flora of the neighbouring continent 

 they form but -^, and of that of the whole globe -^. The amount of 

 peculiarity is also very large, though (as in Euphorbiacecc) the new species are 

 found under a very few genera; in this case 11 of the 15 are such, belong- 

 ing to three genera, of which one, Borreria, alone contains 8. This last and 

 Euphorbia contain the majority of the weeds of the Galapagos, and are 

 further the two largest Phienogamic genera in the group. 



It is singular to remark to what different genera of plants various islands 

 are indebted for their greatest peculiarity, and how often it is the case that 

 such genera give a character of individuality to the scenery. This is effected 

 in the Galapagos by covering the lower lands with Euphorbia and Borreria, 

 whilst the large genera Scalesia, Croton and Cordia give the conspicuous fea- 

 tures of the vegetation of the higher regions. In like manner in Juan Fernan- 

 dez and St. Helena the most conspicuous, which are also the largest genera, 

 are of Compositce and Campanulacece ; and in the Sandwich Islands Goodeniacew 

 and Lobeliacece ; while in the Society group, on the other hand, out of upwards 

 of 200 genera, Piper is the only one containing as many as 3 peculiar species. 

 This leads me to another remark, that the greater the amount of peculiarity 

 an insular flora presents, the closer relationship do the species it contains 

 bear to one another. This is best shown by observing the proportion that 

 the species bear to the genera, which more frequently contain several species 

 in the peculiar than in the borrowed floras. This may be stated in another 



