548 



VEGETATION OF THE DEVONIAN PERIOD. [Ch. XXVI 



Fig. 618 



Psilophyton princeps. Dawson, Geol. Quart. Journ., vol. xv., 1863 ; and Canada Survey, 



1863. Species characteristic of the whole Devonian period in North America. 

 A. Psilophyton princeps, plant restored by Dawson. /. Stem, twice natural size. 

 A&. Ehizome, or underground root-like stem. g. Termination of branches. 



Ac. Cylindrical rootlets. h. Crozier-like, or circinate vernation. 



d. Ehizome. i. Fructification. 



e. Areole of rhizome. 



gen ; but with this single exception the American Devonian flora 

 affords, like the Carboniferous, no evidence of the existence of plants 

 of higher organization than the gymnosperms. 



The monotonous character of the Carboniferous flora might be ex- 

 plained by imagining that we have only the vegetation handed down 

 to us of one set of stations, consisting of wide swampy flats. But 

 Dr. Dawson supposes that the geographical conditions under which 

 the Devonian plants grew were more varied, and had more of an up- 

 land character. If so, the limitation of a flora represented by so 

 many genera and species to the gymnospermous and cryptogamous 

 orders, and the absence of plants of higher grade, admit of no expla- 



