Botany and Zoology. 



431 



parison of different countries in respect to those natural orders which 

 abound most in species ; and Chap. 23, as regards their most characteristic 

 natural families. Chap. 24, on the variety of vegetable forms in different 

 countries and in the world at large, i. e., the probable number of species ; 

 the proportion of genera to species, and of orders to genera and species. 

 Chap. 25, the division of the earth's surface into natural botanical regions. 

 Chap. 26, sketch of the vegetation of different countries in respect to the 

 probable origin of their existing species, &c. 



The Fourth Book, of a single brief chapter, consists merely of a sum- 

 mary of the author's general conclusions. We give these entire, for con- 

 venience availing ourselves of a translation in Hooker's Journal of Botany.* 



"The plants now inhabiting the globe have survived many changes, 

 geological, geographical, and, latterly, historical. The history of their 

 distribution is hence intimately connected with that of the whole vege- 

 table kingdom. 



To explain existing facts, it is fortunately unnecessary to adopt any 

 conclusion upon the most obscure hypotheses of Cosmogony and Palae- 

 ontology, or on the mode of creation of species, the number originally 

 created, and their primitive distribution. Botanical Geography can indi- 

 cate certain probabilities, certain theories, but the principal facts in distri- 

 bution depend upon more recent and less obscure causes. It suffices to 

 understand and to allow certain facts and theories, which appear probable, 

 namely, that groups of organized beings under different hereditary forms 

 (Classes, Orders, Genera, Species, and Races), have appeared at different 

 places and at different times ; the more simple perhaps first, the more com- 

 plicated afterwards ; that each of these groups has had a primitive centre 

 of creation of greater or less extent ; that they have, during the period of 

 their existence, been able to become more rare or common, to spread more 

 or less widely, according to the nature of the plants composing them, the 

 means of propagation and diffusion they are possessed of, the absence or 

 presence of animals noxious to them, the form and extent of the area they 

 inhabit, the nature of the successive climates of each country, and the 

 means of transport that the relative positions of land and sea may afford ; 

 that many of these groups had become extinct, whilst others have 

 increased, at least as far as can be judged from comparing existing epochs 

 with preceding ones ; and lastly, that the latest geological epoch the 

 Quaternarj?-, (that which preceded the existence of man in Europe, and 

 which followed the latest elevation of the Alps), has lasted many thou- 

 sand years, during which important geographical and physical changes 

 have affected Europe and some neighboring countries, whilst other regions 

 of the globe have suffered no change, or have been exposed to a different 

 series of changes. 



"Thus the principal facts of Geology and Palaeontology, reduced to the 

 most general and incontestible, suffice to explain the facts of Botanical 

 Geography, or at least to indicate the nature of the explanation, which it 

 requires the progress of many sciences to complete. 



* We take this occasion to commend to our readers the detailed notice of De Can- 

 dolle's work, given last spring, and summer, in a series of the numbers of Hooker's 

 Journal. It comprises a careful abstract of these volumes, and a critical commentary 

 upon many points, abounding in acute and original remarks. 



