102 OUTLINES OF EVOLUTIONARY BIOLOGY 



FiG. 48. The Sporophyte Generation of a Fern, Aspidium filix mas. (From 



Strasburger.) 



A, section through a sorus or group of sporangia, covered by the indusium ( x 20, after 

 Kny) ; B, lower surface of a pinna, showing the indusia covering the sori ; C, lower 

 surface of a pinna with the sori exposed. 



