4i8 



THE VASCULAR PLANTS 



Fig. 209. — Aspidium, a common fern. A, the entire plant, showing the rhizome, 

 the coiled young leaves arising from it, and three mature fronds, one of which 

 shows sori as dark dots on the under surface. B, a leaflet, showing the shield- 

 like coverings (indusia) of the sori. C, section through a sor'us and the leaf which 

 bears it, as seen through a microscope ; i, the indusium ; s, the sporangia. D, a 

 sporangium, showing the annulus and two escaping spores. — AJter Wossidlo. 



