U 



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, 

 a b c d 



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

 side and top views ; c. colony of Gomfihonema, with branched stalks attached to an 

 alga;y, g, single cells of same, more magnified, top and side views; A, colony of 

 Diatoma, ihe cells connected into a zigzag band ; t, k, colony and individuals (top 

 and side views) of Fragillaria : /, «/, >i, Cocconema. In m the pair is surrounded 

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

 cells (auxosporesi which has been completed in «.— 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 



