• 98 " ■ AQUATIC MICROSCOPY FOR BEGINNERS. 



little balls of translucent jelly often found studding 

 leaves of grass or other objects in the water. 



The following have been partly described in the 

 Key on a preceding page. 



r. ScENED#,SMUS (Fig-. 7g). 

 , The cells are usually four, attached together by their 

 long sides. The spines on the narrow ends of the two 

 terminal cells are curved towards each other, and a 

 spine sometimes grows from the middle of one of the 

 central cells. The plant is common. ^S'. cauddtus, 

 Fig. 79. ' 



Fig. 79. — Scened^smus cauddtus. Fig. 80. — Pedidstrum Boryanum. 



2. PediAstrum (Fig. 80). 



The green cells are usually so arranged as to leave 

 narrow- colorless bands between them, and occasion- 

 ally, in those species formed of a great number of ad- 

 herent cells, several apparently empty colorless spaces 

 are scattered about the disk. In the latter cases the 

 marginal teeth, which are always colorless, are often 

 numerous but they are usually more or less conspicu- 

 ously arranged in groups of two each. In the species 

 here figured the marginal teeth are generally twelve in 

 number. P. Boryanum, Fig. 80. There are about a 

 dozen known species in this country. "Most of them 

 are not rare. 



