78 MICROSCOPY FOR BEGINNERS. 



Some Species of Closterium. 



1. Ends not lengthened out into a colorless beak (a). 



2. Ends lengthened out into a colorless beak (/"). 



a. Back slightly convex, the whole cell slightly 

 curved (&). 



a. Back strongly convex, ventrum nearly straight (<?). 



a. Back strongly convex, ventrum strongly concave, 

 with a central enlargement (<rl). 



a. Back strongly convex, ventrum without a central 

 enlargement (e). 



J. Ventrum nearly straight ; vacuoles close to the 

 rounded ends ; fifteen or twenty chlorophyl glob- 

 ules in a central longitudinal row in each semi- 

 cell. C. linedtum, Fig. 22. 



Fig. 22. Closterium line&tum. 



Ventrum nearly straight ; body tapering towards 

 the rounded, sometimes curved, ends ; vacuoles 

 small, often scarcely visible. C.juncidwn, Fig. 23. 



Fig. 23. Closterium jnncidnm. 



b. Yentrum and back equally curved ; ends tapering ; 



ten to fourteen chlorophyl globules in a central, 

 longitudinal row in each semi-cell; vacuoles very 

 small. C. acerosum. Fig. 2-i. 



c. Ends rounded ; chlorophyl often arranged in nar- 



