IV.] FILICES. 345 



microscopic doubly-coated cells (spores) destitute of an 

 embryo, but capable of developing a small green leafy 

 expansion (prothallus) bearing the essential Organs of Re- 

 production. 



Type — Asptdium {Nephrodiuiti) molle. 



Fig. 226. Asfidium {Nephrodiu7}t) molle, much reduced. 



A perennial herb with a short ascending rhizome, bearing 

 a terminal tuft of large, annual, broadly lanceolate, thinly 

 pilose, bipinnate fronds, two to four feet in length. 



Upon the under surface of the fertile fronds the fruc- 

 tification is arranged in small globose clusters, which are 

 brownish when ripe. These clusters are called sort 

 (each cluster a sorus), and there are usually two rows 

 of the sori upon, at least, the low^er lobes {pinnules) of 

 each of the pinncB of the frond. Occasionally only the 



