418 BOTANICAL GEOGRAPHY. 



,4. BOTANICAL GEOGRAPHY. 



R. B. Hinds has continued his general observations 

 upon botanical geography (see Annual Report for 1842) 

 during the past year (Memoirs on Geographic Botany, 

 Ann. Nat. Hist. vol. xv) ; like the former, however, 

 they contain little more than already known facts and 

 views, not unfrequently mingled with errors, both as 

 regards the facts and deductions. 



The present papers contain, e. g. estimates of the whole number of plants 

 known ;* remarks upon centres of creation, the existence of which the 

 author denies ; on the distribution of certain families ; on the mean area of 

 the extension of each species ; elements for the comparison of two floras ; 

 on physiognomy, &c. I shall only enter upon the consideration of one of 

 these views, and that because it places a simultaneous work by Forbes, re- 

 markable for its originality, in a proper light. The old hypothesis of a single 

 centre of creation, from which all plants upon the earth were distributed, as 

 also the later supposition, that tliis migration of organisms originated in one 

 or a few centres, Hinds opposes by the general law, that wherever plants 

 met with the conditions necessary for their existence, the present vegetation 

 was originally produced. He does not admit, in opposing every migration of 

 plants, even such variations in the original state as would cause the extirpation 

 of individual species, and their disappearance from among the number of 

 living organisms ; whilst such an event, e. g. in the case of the endemic 

 plants of St. Helena, has been as satisfactorily determined as in that of 

 Didus ineptns. The historical change in the constituents of forests, and the 

 migration of individual plants which is in progress before our eyes, and is 

 not merely produced by man, are incompatible with a law expressed so 

 generally. The fact that certain islands in the Indian Ocean, as e. g. Darwin 

 showed, contain only plants which have been washed on shore, by wliich they 

 are thickly covered, whilst the islands in their vicinity possess an endemic 

 vegetation, contradicts the supposition of the existence of a generally diffused 

 productive force, or at least limits it to distinct creative epochs. When we 



* Hinds estimates the number of known plants at 89,170; those existing 

 on the earth at 134,000 species. His statements are founded upon the 

 number of species contained in the first four volumes of De Candolle's 

 ' Prodromus.' These amount to 20,100 ; of which 3875 are Leguminosce, 

 1631 Rubiaceje, 1009 Umbellifera, 990 Cruciferje, 759 Caryophyllaeeaj, 715 

 Myrtacese, &c. 



