EXPLAXATIOX OF PLATE XX. 



SCIIIZvEA. Plant of S. pusilla, of the natural size ; ( 1 ) a fertile pinna with 

 eleven sporangia, magnified; and (2) a separate sporangium, more mag- 

 nified. 



LYGODIUM. (1) Summit of frond of L. palmatum, with fertile and sterile 

 divisions; (2) a fruiting lobe enlarged, with two of the lower scales, or 

 imlusia, removed, displaying a sporangium under each; and (3) a spo- 

 rangium more magnified. 



OSMUNDA. (1) Small piece of the frond of <). Claytoniana, with a fertile 

 and a sterile pinna; (2) a portion of the fruit magnified; and (3) one spo- 

 rangium more magnified. 



IV >TRYCHIUM. Plant of B. ternatum, and (1) a portion of the fruit, with 

 six sporangia, magnified. 



OPIIIOGLOSSUM. Frond of O. vulgatum, and (1) a portion of the fruit- 

 ing spike enlarged. 



