298 



FORMS OF FILICALES 



from Aspleninm in having the sori arranged in chain-like rows 

 parallel to its midrib (Fig. 225, B). In several genera of ferns 

 the indusium is partly or entirely inferior. Thus in the bladder 

 fern, Filix, the partly inferior indusium covers the circular sorus 

 like a hood (Fig. 225, D), while it is wholly inferior in the 

 hay-scented fern, Dennstaedtia, forming a cup (Fig. 225, E) 

 and in Woodsia the indusium is roundish or star-like (Fig. 225, 

 F). Several ferns are distinguished by false indusia that are 

 formed by the more or less modified margins of the leaf. In 

 the bracken, Pteridium, the entire membranous margin of the 

 leaf curves over the closely crowded sori (Fig. 226, A), and in 



FIG. 226. Ferns without indusia or possessing false ones: A, leaflet of 

 bracken fern, Pteridium. B, maiden-hair fern, Adiantum. C, polypod 

 fern, Polypodium. After Sprague. 



the maiden-hair fern, Adiantum, the sporangia are at the ends 

 of the veins and covered by reflexed portions of the leaf (Fig. 



