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this hypothetical observation, that the first vegetable types, or at least the 

 dicotyledonous ones, have appeared, at the same or at different times, not only 

 at different places but with different original characters, constituting here 

 and there distinct groups without homogeneity or relation of forms. Consider- 

 ing what is known of the succession of these groups, it seems as if some of 

 the original types had persisted more or less indefinitely in the scries, being 

 modified perhaps by casual circumstances ; and as if other original forms or 

 prototypes had appeared here and there and multiplied the characters of the 

 vegetable groups. Indeed, this second supposition is a mere corollary of the 

 former. 



But this touches the question of the origin of species, which cannot be 

 considered now, especially because the materials for the basis of a discussion 

 of this kind are as yet too scant. Schimper, in his great work, (Puleonlologie 

 vegetate,) describes, indeed, nearly six thousand species, distributed under 

 eight hundred and fifty genera of plants, known from fossil remains of all 

 the geological formations. But what is this compared to what is known of 

 the flora of this epoch, of which many hundreds of thousands of species are 

 described under more than fourteen thousand genera] Of the old floras, 

 especially of those of this continent, we know scarcely a diminutive fraction. 

 The task of the paleontologist is, therefore, and must be for a long time to 

 come, that of a mere recorder of facts. It is in this point of view that this 

 monography of the plants of the Dakota group has been prepared, and may 

 be considered of some advantage to science. 



