398 THEORY OF PROGRESSION chap. xx. 



earth more jviid more liiglily organized tj'pes of animal and 

 vegetable life; the modern species being, on the whole, more 

 specialized, i.e. having separate organs, or parts of the body, 

 to perform different functions, which, in the earlier periods 

 and in beings of simpler structure, were discharged in com- 

 mon by a single part or organ. 



Professor Adolphe Brongniart, in an essay published in 

 1849, on the botanical classification and geological distribu- 

 tion of the genera of fossil plants,* arrives at similar results 

 as to the progress of the vegetable world from the earliest 

 periods to the present. He does not pretend to trace an 

 exact historical series from the sea-weed to tlie fern, or from 

 the fern again to the conifers and cycads, and lastly, from those 

 families to the palms and oaks, but he, nevertheless, points 

 out that the cryptogamic forms, especially the acrogens, pre- 

 dominate among the fossils of the primarj^ formations, the 

 carboniferous especiall}", while the gymnospei^ms or coniferous 

 and cj^cadeous plants abound in all the strata, from the Trias 

 to the Wealden inclusive; and. lastly, the more highly deve- 

 loped angiosperms, both monocotyledonous and dicotyledon- 

 ous, do not become abundant until the tertiary period. It 

 is a remarkable fact, as he justly observes, that the exogens, 

 Avhich comprise four-fifths of living j)lants, — a division to 

 which all our native European trees, except the Conifera}, 

 belong, and which embrace all the Compositse, Leguminosa>, 

 Umbellifera3, Crueifene, Heaths, and so many other families, 

 — are w^iolly unrepresented by any fossils hitherto discovered 

 in the primary and secondary formations from the Silurian 

 to the oolitic inclusive. It is not till we arrive at the creta- 

 ceous period that they begin to appear, sparingly at first, and 

 only playing a consj^icuous part, together with the palms and 

 other endogens, in the tertiary epoch. 



* Tableau des Genres de Vegetans fossiles, ic. Dictionnaire Universel 

 d'llistoire Naturelle. Paris, 1849. 



