DEVELOPMENT OF PLANTS 



329 



by an indusium that is laterally attached at a single point (Fig. 

 222, A). The Christmas fern, Polystichum, has a circular sorus 

 with centrally attached indusium (Fig. 225, C). The spleenwort 

 fern, Asplenium, is characterized by elongated sori arranged 

 obliquely to the midrib upon the upper side of the veinlets. 

 The indusium is attached on one side of the sorus along its entire 

 length (Fig. 222, B). The chain fern, Woodwardia, differs 

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



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

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

 Polypodium. — ^After Sprague. 



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). 



