14 



PLANT LIFE. 



cilia are protruded into the water outside. Tlie 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, 

 "■he a 



a 



Fig. 20. ^Various diatoms, a, Syicdra : b, Plejn'nsi^Dia ; it, d, GriDumatophora, 

 side and tup views ; c, colony o£ Gomphoneina^ with branched st;ilks attached ti> an 

 alg-a ; y, g\ single cells of same, more magnified, top and side views ; h, colony of 

 DiatoiJia, ihe cells connected into a zigzag band ; /, k^ colony and individuals (top 

 and side views) of Fragillaria ; /, i>ty «, Coccoiteina. In m 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 >i. — After Kerner. 



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

 toms are very \arious in form, and present t\A'o different 

 aspects. When seen from the side thev are generally ehm- 

 gated-rectangular. When looked at from al)o\e they are 

 short-cylindric, disk-shaped, l)oat-sha[H'd, or varionsly curved 



