H 



PLANT LIFE. 



cilia are protruded into the water outside. The lashing of 

 these rolls the whole colony about. Each vegetative in- 

 dividual is entirely like the others, but those connected 

 with reproduction become specialized. 



Diatoms and desmids, 

 21. Shelled plants. — Other one-celled plants constitute a 

 group known as diatoms, found in both fresh and salt waters, 



Fig. 20. — Various diatoms, a, Synedra ; 6, Pleurosigma ; c, d, Grammatophora, 

 side and top views ; e, colony of Gomphonema, with branched stalks attached to an 

 alga ; f, Si single cells of same, more magnified, top and side views; h, colony of 

 Diatoma, the cells connected into a zigzag band ; t, i, colony and individuals (top 

 and side views) of Fragillaria ; /, M, «, Cocconema. In ;« the pair is surrounded 

 by jelly preliminary to the escape of the protoplasm and the formation of two new 

 cells (auxospores) which has been completed in n. — After Kerner. 



either attached or free-swimming (figs. 20, 21). The dia- 

 toms are very various in form, and present two different 

 aspects. When seen from the side they are generally elon- 

 gated-rectangular. When looked at from above they are 

 short-cylindric, disk -shaped, boat -shaped, or variously curved 



