IV] LOWER AND UPPER DEVONIAN FLORAS 51 



all is that, if we regard Psilophyton as a reduced Cormophyte, 

 all the other Procormophytes such as Arthrostigma, Thursophyton, 

 etc. must be likewise regarded as reduced Cormophytes. This is 

 clearly not the case and there is thus every reason to regard the 

 Psilophyton flora as primitive and not reduced, especially as it 

 can be shown that more highly evolved types sprang from them 

 (see Chapter VI of this memoir). 



Further, we know of no geological reasons which would lead 

 us to suppose that the conditions of existence of plant life were 

 at all different in Lower and Upper Devonian times. In the 

 later epoch, members of the Psilophyton and Archaeopteris 

 floras, as we have seen (pp. 9, 10), existed side by side, and wer^ 

 the latter in existence in Lower Devonian times there would 

 seem to have been nothing to have prevented |;hem from 

 flourishing equally well at that period. As a matter of fact they 

 did not then exist, for the incoming of the Archaeopteris flora 

 is plainly indicated in Middle Devonian times, and it was clearly 

 not established until the latest epoch of that period. 



