GENERAL RELATIONS OF PLANTS TO TIME. 4/5 



plants, and embracing representatives of almost all the great 

 groups of plants which at present grow upon its surface. Thus, 

 we find in the Devonian Rocks representatives of the groups of 

 the Horse-tails, Club-mosses, Ferns, and Gymnospermous and 

 Angiospermous Exogens. We have, however, no certain re- 

 presentative of the great group of the Endogens, whilst the 

 Angiospermous Exogens are known by a single genus only, 

 represented by a single species. Upon the whole, therefore, 

 the vegetation of the Devonian period is characterised by the 

 predominance of Cryptogams and Gymnospermous Exogens. 



Passing on to the Carboniferous period, we have to consider 

 the largest and most varied of the Palaeozoic floras, but one 

 which is in most respects very similar to that of the Devonian 

 period. Some Devonian genera of plants do not pass up into 

 the over-lying formation, and some of the Carboniferous genera 

 have not been recognised in the Devonian ; whilst hardly any 

 species are common to the two floras. Still, the general fades 

 of the Carboniferous vegetation is much the same as that of 

 the Devonian ; and the same groups predominate in the former 

 as in the latter, The predominant groups of plants in the Car- <f , 

 boniferous Rocks are the Ferns (Filices), the Sigillarioids, the 

 Lepidodendroids, and the Calamites, of which all except the 

 Sigillarioids are certainly Cryptogams. Here, also, we have 

 the first instance of the occurrence of a Fungus (Archagari- 

 a>n). The Conifera are well represented by several genera 

 (Araucarioxylon, Dadoxylon, &c.), but no remains of trees 

 belonging to the Angiospermous Exogens have been as yet 

 detected. There are, however, a few flowering plants (such as 

 the Monocotyledonous Pothocites of the Scotch Carboniferous). 

 Lastly, the Carboniferous Rocks have yielded remains of the 

 genus Nwggerathia, referred by Brongniart to the peculiar Gym- 

 nospermous group of the Cycadacetz, but regarded by others as 

 belonging to the Ferns. 



In the Permian period, the vegetation is nearly related to 

 that of the Coal-measures. We have still numerous Ferns 

 (Neuropteris, Pecopteris, Sphenopteris\ Tree-ferns (Psaronius\ the 

 Lycopodiaceous Lepidodendron, and Calamites. The Conifers, 

 also, are abundant, and belong to several genera. Some of the 

 Conifers, however (as Ullmania), bear genuine cones, and the 

 Sigillarioids, which are so characteristic of the Carboniferous 

 period, have apparently altogether disappeared in the Permian. 



With the Trias we commence the great series of Mesozoic a& 

 deposits, and there is a marked change in the vegetation of this 

 period as compared with that of the Carboniferous and Permian 

 epochs. The Lepidodendroids and Sigillarioids have now com- 



