FILICES 



73 



apical portion, and they then assume a great variety of shapes circular, 

 reniform, crescent-shaped, linear, or they are concealed beneath the 

 revolute margin of the leaf. The sorus may or may not be covered by 

 a membrane called the indusium, an outgrowth of the epiderm. In the 



FIG. 51. Asplenium Adiantum-nigrum L. ; rhizome with fronds showing Circinate 



Asplenitun Adiantum-nigniin L. ; rhizome with fronds showing drcii 

 irnation (natural size), a, under side of fertile pinnule (magnified). 



Cyatheacese they assume the form of a cup ; in the Hymenophyllaceae 

 they are situated at the extremity of a vein at the apex or margin of a 

 pinna. In some instances, as in our native ' flowering ' or ' royal fern ' 

 .(Osmunda regalis, L.), the sori completely consume, in the course of their 



