DESMIDS, DIATOMS, AND FRESH-WATER ALG^. 105 

 



2. ANAB.ENA (Fig. 83). 



Filaments moniliform, freely floating, the cells spheri- 

 cal, the larger scattered ones globular, yellowish. The 

 filaments are often curved, and sur- 

 rounded by a delicate mucous mate- 

 Fig. 83.-Anab.ma. r j al> ^^ &TQ geveral spec i es w hi c h 



closely resemble each other (Fig. 83). 



3. OSCILLARIA (Fig. 84). 



These plants are found almost everywhere in the wa- 

 ter. They often form thick floating mats of a dark 

 purplish almost blackish color, or they are entangled 

 among other plants in a dark green film. Under the 

 microscope they consist of filaments composed of very 

 many short cells that vary a good deal in width accord- 

 ing to the species, of which there are several. They 

 can usually be known by the bluish-green color and 

 their characteristic motions. Some are like straight 

 rods of cells bending slowly from side to side ; others 

 twist and writhe and coil them- 

 selves into circles, only to slowly 

 uncoil and repeat the move- 

 ments. Some glide slowly for- 

 ward, the tip end gradually bend- 

 ing and curving. The move- 

 ments, when the plants are in a healthy condition, are 

 incessant. The beginner need never be at a loss to rec- 

 ognize one of the several species of Oscillaria. Three 

 forms are shown in the figure. (Fig. 84.) 



