DIV. I 



PTERIDOPHYTA 



507 



leaves of Polypodium vulgare are pinnate, and spring singly from 



FIG. 471. Dryopteris (Aspidium) filix mas (f nat. size). A, Sorus in vertical section, (x 20. 

 After KNY.) B, Pinna with young sori still covered by the indusia. C, Somewhat older sori 

 with withered indusia. (Slightly magnified.) OFFICIAL. 



