1896 THE MICROSCOPE. 35 



apply a cover-glass and sufficient water to exclude tlie 

 air, being careful to admit no more. Diatoms and some- 

 times desmids and algge are found in this way. 



Alga3 are seldom found in deep water, but in pools and 

 slowly running streams. They most often attach them- 

 selves to plants, sticks or stones. They are usually green 

 but may be brown or purple and are surrounded by a 

 jelly-like substance. A form quite common is 8cenedes- 

 mus quadricauda (fig. d), which consists of four green 

 cells attached by their long sides and having spines pro- 

 jecting from the four corners. Pediastrum granulatum 

 (fig. a) consists of a disk having marginal teeth arranged 

 in twos and containing six or eight green cells separated 

 by colorless bands. Figure a also shows an alga. 



All the species of the desmid Closterium are more or 

 less crescent shaped, and are usually green. Each end 

 often contains a clear vacuole in which many small dark 

 particles may be seen swarming. Closterium linula, 

 (fig. m) has the ends rounded and containing vacules. 



It also shows the protoptasmic movement Ijctween the 

 cell-wall and the coloring matter. It has dark longitu- 

 dinal bands, 



Volvox, another desmid, is a small sphere which is con- 

 tinually revolving. When examined under a high power, 

 it is seen to be studded with points, each point having 

 two cillia which are in constant motion. It is this which 

 causes the revolutions. Dark green balls are sometimes 

 seen inside the globe. These are young plants and when 

 matured the mother plant bursts and they escape. Vol- 

 vox globator is represented in figure c. Cocconema 

 lanceolatum (fig. b) illustrates a branched diatom with 

 the frustule on the end of the stem. The frustles often 

 float free and have a median longitudinal line with a 

 nodule in the center and at each end. Clomphonema ac- 

 cuminata (fig. t) is another branched form. The frustules 

 are wedge-shaped with the narrowest edges attached to 



