FOSSIL VASCULAR CRYPTOGAMS 



123 



.blance to Polypodiace^ and Cyatheace^ among existing forms. No 

 fructification resembling that of Osmundaces has at present been dis- 

 covered ; but Osmundites (Carruth.), from the Lower Eocene, has been 

 referred to that order by its discoverer from the pecuharities of the 

 structure of the stem. The Ophioglossaceae are still unrepresented in 

 palseophytology. 



The internal structure of the stem and leaf-stalk of most fossil ferns, 



Fig. 95. — Section of Stemmatopieris Cord, invested with TOots= Psaronins Cord. 

 (From a specimen in the British Museum.) 



where this can be determined, differs in no important respect from that 

 of living forms. We find the same interrupted ring of 'vascular' 

 bundles, which may be either concentric or collateral, the xylem con- 

 sisting largely of scalariform tracheides, the same layers of sclerenchyme 

 both in connection with the bundles and beneath the epiderm ; evident 

 indications of gum-passages have even been detected. But though this 

 is by far the most common type of structure, a second is di.splayed in a 

 few rare examples, in which the arrangement of the ' vascular ' elements, 



