146 INTRODUCTION TO PLANT GEOGRAPHY [CHAP. 



The pre-Cambrian and early Palaeozoic preceding the Devonian 

 together represent probably more than nine-tenths of known geologic 

 time and constituted the age of Schizophytes, Thallophytes, and 

 invertebrate animals. Bacteria, Blue-green Algae, Fungi, and true 

 Algae of various groups appear to have been the main plants living 

 through most of this time, although towards the end of it, in the 

 Silurian, there seem to have been added the first land-plants in the 

 form of some primitive Psilopsida and Lycopsida, and the still more 

 problematical Nematophytales. 



The Devonian and Carboniferous periods constitute the real age 

 of Pteridophytes and Fishes, even if these groups had an earlier 

 origin. Thus in the Devonian the primitive groups already men- 

 tioned apparently continued to flourish, as have Bacteria, Fungi, and 

 Algae to the present day, while there were added various Sphenop- 

 sida, etc. Apparently none of these early Pteridophytes has sur- 

 vived, at least at the generic or lower level, any more than have the 

 primitive Ferns which first appeared in that period, or possibly 

 the Gymnosperms which were well established before the end of the 

 Carboniferous. Although the early Devonian is often spoken of as 

 primarily psilophytinean, there appear to have been plentiful other 

 Pteridophytes living at the time. These evidently became more 

 diverse and numerous in the upper Devonian, when the Psilophytales 

 seem to have died out, and by then to have included some of tree 

 dimensions. These may show what appear to be annual rings and 

 indicate marked seasonal changes. An attempted reconstruction of 

 a late Devonian forest is shown in Fig. 38. 



The Carboniferous period was the culmination of the age of 

 Pteridophytes, including inany of large tree form as indicated in the 

 diagrammatic reconstruction (Fig. 39). To these the Lycopsida, 

 Sphenopsida, and Filicineae all contributed, and, in addition, the 

 early gymnospermous Pteridosperms and Cordaitales. The Bryo- 

 phytes first appeared at this time, at least so far as known indubitable 

 fossils are concerned, as did several of the modern groups — including 

 the true Club-mosses, Horsetails, and some Ferns — while before its 

 end there existed some primitive Conifers. The upper Carboni- 

 ferous or Pennsylvanian was the great Palaeozoic coal age, and 

 evidently a time of damp and widely favourable ' even ' climate in 

 both northern and southern hemispheres. The vegetation which 

 gave rise to the immense coal deposits of the northern hemisphere 

 seems to have been one of the most widely luxuriant of all time, 

 though the coals of the southern hemisphere appear to have been 



