346 FILICES. \cnN\i. 



lower sori of each pinnule are developed, and then they 

 occur in a single row on each side of the midrib of the 

 pinnae. The sori are protected at first by a peltate mem- 

 brane {indusiiim), which at length, withers up exposing the 

 minute-stalked sporanges of which each sorus is composed. 



Fig. 227. Pinnule of Aspidium molle, with a double row of reniform sori. 



The sporanges require examination with a magnifying 

 glass. They will be found to be capsules opening trans- 

 versely, with a vertical elastic ring up the side and over 

 the top, which serves as a hinge. They each contain an 

 indefinite number of spores, which are liberated on de- 

 hiscence of the sporange. 



Many Indian Ferns depart considerably from our Type- 

 species in the form of the frond, the form and arrangement 

 of the sori, the absence of indusium, and in the structure 

 and mode of dehiscence of the sporanges. The difference 

 presented in these respects by some of the commoner and 

 more remarkable Indian genera are noted in the following 

 list. 



■^ Sporanges distinct {jiot cohering), and provided with 

 a more or less distinct ring (annulus). 



(a.) AnnuliLS vertical. 

 Polypodium. — Sori on the under surface of the frond, 

 nearly or quite round. Indusium o. 



