CH. iij THE TWO FLORAS 9 



we shall show here, are of an entirely different morphological 

 nature. By the time we reach the Upper Devonian, these newer 

 types, the Archaeopteris flora, have become dominant in their 

 turn. Archaeopteris, Sphenophyllum, Boihrodendron, among 

 many other genera, are all clearly Pteridophyta. The members 

 of the Psilophyton flora were Thallophyta, as we hope to show 

 here. 



In Upper Devonian times, some members of the Psilophyton 

 flora were still in existence, though in greatly reduced number 

 and in a position of subordination to the dominant Archaeo- 

 pteris flora. By the time we reach the next higher series, the 

 Lower Carboniferous rocks, the Psilophyton facies has entirely 

 disappeared. On the other hand, during this period, the 

 Archaeopteris facies reaches its maximum development, and it 

 persisted unchallenged as regards dominance until the close of 

 this epoch, while many survivals lingered on even into Coal 

 Measure times. We have then, in the Lower Devonian, a very 

 ancient land flora, which in ]\Iiddle and Upper Devonian times 

 was gradually displaced by a new flora which only reached its 

 maximum development in the earlier part of the Carboniferous 

 epoch. Thus, while the flora of the Upper Devonian is essentially 

 of the Carboniferous facies, that of the Lower Devonian is of 

 a quite different archaic type. The following table shows the 

 distribution in Devonian time of the two floras. 



A Summary of the Chief Genera of the Axchaeopteris and 

 Psilophyton Floras with their distribution in Devonian Time. 



Archaeopteris Flora Psilophyton Flora 



Sphenophyllum \ „ , ., Psilophyton 



Pseudobornia j »Phenopsida Ptilophyton 



Psygmophyllum Palaeophyllales Thursophyton 



< Archaeopteris i Barrandeina 



I Rhacopteris \ Barinophyton 



> Sphenopteris I Taeniocrada 



Sphenopteridium f " ^ 



S Cephalopteris 

 g ? Cordaites I 



^ Bothrodendron \ 



Archaeosigillaria [-Lycopsida 

 Leptophloeum ) 



