THE MALE FERN 



147 



kidney-shaped; this is termed the indusium. Thus, we 

 understand that each brown point found on the under 

 surface of the frond is a sorus, consisting of a cluster of 

 sporangia protected by the indusium. We need the 

 aid of a powerful hand lens to make out the sporangia; 

 a goodly number being clustered in each sorus, they 



Fig. 44. 



A, Frond of male fern; B, underside of a fertile pinna; a, rachis; s, sorus. 



Enlarged. 



are necessarily small. Now, the sporangia yield a 

 great number of spores, and we may rest assured that 

 if every spore produced by a single Male Fern were per- 

 mitted to yield a complete plant, the species would soon 

 be uncomfortably numerous; but " there's many a slip 

 'twixt the cup and the lip " in the plant realm, and so 



