FILICES. 



377 



furnished with a usually incomplete, nearly vertical, or rather oblique 

 ring. Receptacle prominent, barrel-shaped (Fig. 265). Tree-ferns. 

 Genera three (CyatJwa, Hemittlia, and Alsophila) ; species 150, mostly 

 tropical and subtropical. 



4. Polypodiactce. Sporangia stalked, splitting transversely, fur- 

 nished with a usually incomplete vertical ring. Receptacle not prom- 



FIG. 263. 



FIG. 264. 



FIG. 265. 



Fig. 263. Portion of a leaf of Gleichenia, with a sorus, a ; b, a sporangium. Af- 

 ter Hooker. 



Fig. 264. Portion of a leaf of Trichomane*, a, with five sori ; b, a sporangium. 

 After Hooker. 



Fig. 265. Vertical section of a sorus, a, of Alsophila, showing the cylindrical re- 

 ceptacle ; b, a sporangium. After Hooker. 



inent (Figs. 2576 to 261). Genera fifty (Acrostichum, Polypodium, 

 Adiantum, Pteris, Axplenium, Sculopendrium, Aspidium, Cyslopteris, 

 etc.) ; species 2000, widely distributed throughout the world. 



5. Osmundacece. Sporangia stalked, splitting vertically, furnished 

 with only a faint horizontal bar, instead of a ring (Fig. 266). Genera 

 two (Osmuiida and Todea) ; species ten to twelve, widely distributed in 

 north and south temperate re- 

 gions. 



6. Sch'zceacece. Sporan- 

 gia sessile, splitting vertical- 

 ly, crowned by a complete 

 email annular horizontal ring 

 (Fig. 267). Genera five 

 (Schizcea, Anemia, Lygodium, 

 etc.); species sixty, mostly 

 natives of the warm regions 

 of America and Asia. 



Economically the true Ferns are of comparatively little value. The 

 pulpy interior of the stem of a tree-fern (Cyathea meduttaris) growin'g 

 in the Pacific islands furnishes an important article of food to the 

 natives. In Australia the underground stems of Pteris aquilina 

 supply an indifferent food. A few species are of doubtful value as 

 astringent medicines. The long woolly hairs of certiiin species ot 



Fig. 266. Two sporangia of Osmunda; a, 

 with the rudimentary ring wen in front view ; 

 b, with the ring seen in profile. After Hooker. 



Fig. 267. Lower portion of a fertile pinna, a, 

 of Schizcea ; b, a sporangium. After Hooker. 



