312 PHYSIOLOGICAL BOTANY. PART II. 



Graminese are the chief Monocotyledones ; and there are 

 several Dicotyledones which have been considered analo- 

 gous to Apocynete, Euphorbiacete, Cacteae, Coniferae, 

 &c. No great stress need be laid at present upon the 

 several proportions which species of these classes bear 

 to each other ; as it is probable that subsequent re- 

 searches will considerably modify them. The great pre- 

 dominance and size of arborescent ferns and other tribes of 

 Ductulosa? constitute the main feature of the formation. 



Above the coal we arrive at the new red sandstone ; 

 in some of the formations subordinate to this series a 

 few species of fossil plants occur. In the oolitic series 

 they become more abundant, and some beds are re- 

 markably characterized by the prevalence of the genus 

 Zamia, together with some Conifera?, Liliacea?, and 

 many ferns, the latter being very distinct from those in 

 the former formations. In the green sandstone and 

 chalk few species have been hitherto found, and these 

 are almost all marine. Among the tertiary strata (or 

 those above the chalk) the Dicotyledones begin to pre- 

 vail to a far greater extent than they did before, and 

 the plants are entirely different, including, terrestrial, 

 lacustrine, and marine species. Several fruits are 

 referable to existing genera, as Acer, Juglans, Salix, 

 Ulmus, Cocos, Pinus, &c. 



It is remarkable that scarcely any species has been 

 found in more than one distinct formation, and none 

 have occurred in any two which are separated by a long 

 epoch. Hence it appears to be a natural conclusion, that 

 there have been successive destructions and creations of 

 distinct species. Mons. Brongniart has grouped the 

 several formations in which vegetable remains are 

 found, under four great epochs, during each of which 

 no very marked transitions occur in the general cha- 

 racter of the vegetation ; but between any two of these 

 epochs, a striking and decided change takes place : 

 even most of the genera are different, and none of the 

 species are alike. These epochs include the periods 

 during which the following strata were deposited : 



