FIG. 271. A fern (Aspidium marginale) 



A, section of the creeping stem, or rootstock, showing the arrangement of the 

 living fronds around the tip, and the dead stems of last year's fronds farther 

 back. B, a leaflet of the frond viewed from below to show the position of the 

 sori. C, details of the sori and veining on a portion of a leaflet. D, section of 

 a sorus: i, indusium; , sporangia. E, a spore case or sporangium, showing 

 the opening from which the spores (sp) have been discharged ; r, ring 



308 



