MICROSCOPIC OBJECTS. 141 



and small pieces of the frond should be fixed by gum or 

 Canada balsam to black discs about half an inch in 

 diameter. It is important to select these specimens at a 

 proper stage of their growth : if the reproductive organs 

 are too young, they will not be sufficiently developed, 

 while if ripe they soon become brittle ; the elastic ring or 

 case containing the spores break and scatter them; 

 nothing is then left but the remains of the ring or case. 



