INTUODrCIIOX. 



by two genera, Lepidodendrdn and Bothrodendron, while Lepido- 

 phloios, and to some extent also Sigillaria, appear in Lower 

 Carboniferous times. 



The Fern-like plants, whether they be true Ferns (Filicales), or 

 fern-like Spermophytes (Pteridospermeae), are numerous. Only one 

 genus, Adiantites, a characteristic type, is at present known to 

 have belonged to the latter group, while the true affinities of others, 

 such as Archteopteris, Ca/rdiopteris, li/iacopfcn's, and Sphenopten*, 

 have yet to be ascertained. There is, however, evidence, from 

 specimens in which the internal structure is preserved, that the 

 Cycadofilices, of which some members are known to have possessed 

 the seed-bearing habit (Pteridosperms), were not uncommon at 

 this period. 



There remain two important groups, the Sphenophyllales, of 

 which the genus Sphenophyttum is the principal representative, and 

 the Cordaitales, the latter of Gymno<permous affinity, both of 

 which have been long extinct. They have been recorded from 

 the Upper Devonian and the Lower Carboniferous rocks. 



When we pass to the deposits laid down during Upper Carboni- 

 ferous and Permian times, we find these same six groups still 

 dominant types in the vegetation of that epoch, whether in the 

 Northern or the Southern continent. Three new groups make their 

 first appearance. These are the Cycadophyta, including the modern 

 Cycads, a small tropical and sub-tropical family, now the sole 

 survivors of what was once a great class of plants, the Coniferales, 

 and the Ginkgoales, the last-named represented to-day by a single 

 species, Ginkgo biloba. None of these new groups, however, became 

 of real importance in the vegetation of the period which we are 

 considering. They were entirely overshadowed, both in numbers 

 and diversity, by the representatives of the six ancient types, which, 

 as we have seen, were also dominant at an earlier epoch, although 

 in the succeeding epochs of Mesozoic age they in their turn formed, 

 with the ferns, the predominant types of vegetation. 



Having briefly traced the broad features of the vegetation of the 

 most ancient botanical epochs with which we are at all well 

 acquainted, we may now pass on to compare and contrast the various 

 elements of the two floras of Permo-Carboniferous times. The first 

 point to be noticed is that the difference between them does not 

 lie in the botanical types or classes of plants represented in each. 



