EXPLAXATIOX OF PLATE XVL 



POLYPODIUM. — riant of 1'. vnl,i>-arc ; piece of tlie froiul ; a magnified spo- 

 rangium with its stalk, and another bursting and discharging spores. 



ONOCLEA. — ( 1 ) Pinna of the sterile frond of (). Struthiopteris ; (2) portion 

 of a fertile froiul ; ("5) a ])iece of one jjinna cut off to show the manner in 

 which it is rolled uj) ; and (4) a portion of the last, magnified, with one 

 side unrolled; toward the base the s])orangia all removed, to show how 

 the fruit-dots are borne each on the middle of a vein. 



PELLvEA. — Sterile and fertile plants of P. gracilis, and (1) a portion of the 

 fertile frond enlarged, with a piece of the marginal indusium turned back 

 to display the fruit; the sporangia are all removed from the fruit-bearing 

 tips of the two forks of the lower vein. 



