56 



PRACTICAL BOTANY. 



FIG. 28. 1, cells of Synedra ulna attached to a plant cell; 2, a single cell 

 of Synedra ulna more highly magnified ; 3, Navicula liber, side view ; 

 4, Navicula liber, front view; 5, Navicula tumida, front view; 6, Navic- 

 ula tumida, side view; 7, Triceratium favus ; 8, Campy lodiscus spiralis; 

 9, Pleurosigma angulatum ," 10 and 11, Grammatophora serpentina ; 12 

 and 13, Gomphonema capitatum ; 14, Gomphonema capitatum on stalks 

 attached to plant cells ; 15, Diatoma vulgare ; 16 and 17, Fragilaria vires- 

 cens ; 18, Cocconema cistula ; 19, two cells of .Cocconema cistula prepar- 

 ing to form auxospores ; 20, the same after the auxospores have elongated 

 and are preparing to throw off the old cases which are seen on the right 

 and left. 19 and 20 show the cells enclosed in gelatinous sheaths. All of 

 these figures are highly magnified. (Kerner and Oliver.) 



The individual cells are commonly spoken of as frustules. 

 The structure of these frustules is highly characteristic. 

 The foundation of the frustules is cellulose, heavily laden 

 with silica which has been deposited from the water in 

 countless numbers of exquisitely delicate and interesting 

 patterns. Each frustule is made up of two valves, one of 

 which overlaps the other like the cover of a box. (Fig. 26, 

 B and Fig. 27, q.) The junction of th8 two valves is 

 called the girdle. The frustules inclose a mass of proto- 

 plasm containing granules bearing chlorophyl and others 

 bearing the brown pigment that gives the prevailing color 

 to the organisms. 



If gatherings of Diatoms be treated with boiling nitric 



