AS COMPARED WITH THAT OF THE PRESENT DAY. 



411 



ticular species shows it, and would afford material, if fossilized, for 

 many bad species. 



Generally speaking, however, venation is a character of the greatest 



Fig. 7. 



importance ; and to show how closely it should be scrutinized, an illus- 

 tration is added (Fig. 8) of a form of frond and fructification common 

 to two very different ferns, which are permanently and effectually dis- 

 tinguishable by the length of one branch of a repeatedly branched vein. 



Fig. 8. 



The general character of the frond of both A and B is to have the 

 veins alternately simple and branched, the simple one is in both pro- 

 duced only half-way towards the margin, and bears a sorus on its point, 



