VARIATION AND DISTRIBUTION OF SPECIES. 145 



least idea as to how the change from the one to the other 

 comes to pass. But it is interesting, and in this connection 

 perhaps instructive, to remark that, while some dicotyledonous 

 plants hold to the verticillate, L e., opposite-leaved phyllotaxis 

 throughout, a larger number — through the operation of some 

 deep-seated and innate principle, which we cannot fathom — 

 change abruptly into the other species at the second or third 

 node, and change back again in the flower, or else effect a 

 synthesis of the two species in a manner which is puzzling to 

 understand. Here is a change from one fixed law to another, 

 as unaccountable, if not as great, as from one specific form 

 to another. 



An elaborate paper on the vegetation of the Tertiary period 

 in the southeast of France, by Count Gaston de Saporta, pub- 

 lished in " Annales des Sciences Naturelles," xvi. pp. 309- 

 344, — which we have not space to analyze, — is worthy of 

 attention from the general inquirer, on account of its analysis 

 of the Tertiary flora into its separate types. Cretaceous, Aus- 

 tral, Tropical, and Boreal, each of which has its separate and 

 different history, — and for the announcement that " the hia- 

 tus., which, in the idea of most geologists, intervened between 

 the close of the Cretaceous and the beginning of the Tertiary, 

 appears to have had no existence, so far as concerns the vege- 

 tation ; that in general it was not by means of a total over- 

 throw, followed by a complete new emission of species, that 

 the flora has been renewed at each successive period ; and 

 that while the plants of southern Europe inherited from the 

 Cretaceous period more or less rapidly disappeared, as also 

 the austral forms, and later the tropical types (except the 

 Laurel, the Myrtle, and the Chamcerops humilis)., the boreal 

 types, coming later, survived all the others, and now compose, 

 either in Europe, or in the north of Asia, or in North America, 

 the basis of the actual arborescent vegetation." Especially 

 " a very considerable number of forms nearly identical with 

 Tertiary forms now exist in America, where they have found, 

 more easily than in our [European] soil, — less vast and less 

 extended southward, — refuge from ulterior revolutions." The 

 extinction of species is attributed to two kinds of causes : the 



