THE PTERIDOPHYTA : FILICALES, THE FERNS 



;2i 



Fig. 516. — Osmiitida regalis. Plant showing sterile and fertile fronds. 



Much reduced. 



Fig. 5 1 7. — Osmundagracile. Developing fertile 

 leaves showing circinate vernation. 



Anatomy of the Stem 



The stem of the young sporeUng plant is protostelic, but as it matures 

 the stele becomes medullated and the ring of vascular tissue is finally broken 

 into a number of separate strands, which are often U-shaped, with the arms 



