CLASSIFICATION OF THE PTERIDOPHYTES. 117 



spore-bearing division forms a sort of spike, and the sporangia 

 are much less distinct. The sporangia in both differ essen- 

 tially from those of the true ferns in not being derived from 

 a single epidermal cell, but are developed in part from the 

 ground tissue of the leaf. 



FIG. 70. Forms of ferns. A, grape fern (Botrychium) , x l / 2 . x, fertile part 

 of the leaf. B, sporangia of Botrychium, x 3. C, flowering fern (Osmunda). 

 x, spore-bearing leaflets, x %. D, a sporangium of Osmunda, x 25. r, ring. 

 E, Polypodium, x l. F, brake (Pteris), x 1. G, shield fern (Aspidium), x 2. 

 H, spleen-wort (Asplenium), x 2. /, ostrich fern (Onoclea), x 1. J, the 

 same, with the incurved edges of the leaflet partially raised so as to show the 

 masses of sporangia beneath, x 2. 



In the true ferns (Filices), the sporangia resemble those 

 already described, arising in all (unless possibly Osmunda) 

 from a single epidermal cell. 



One group, the water ferns (Rhizocarpece) , produce two 

 kinds of spores, large and small. The former produce male, 

 the latter female prothallia. In both cases the prothallium is 



