174 



THE ALG.E 



must follow the accounts of the groups. However, it is an inter- 

 esting fact that representative algie of these four classes can 

 generally be picked out at a glance by their color alone. 



CLASS I. THE BLUE-UKEEX ALG^, OR 

 CYANOPHYCE.E 



207. The blue-green algae. The simplest types of plants are 

 found among the blue-green algae and in that related group of 



the fungi called 

 the bacteria. 

 Some of these 

 plants are the 

 most primitive 

 forms of life 

 now present on 

 the earth. 



208. The one- 

 celled blue- 



FIG. 173. One-celled blue-green algae and their green algae. 



cell colonies These forms 



A, Glceocapsa, solitary cell and small groups held together ma y develop as 

 by the thick gelatinous envelopes ; B, Clathrocystis serugi- . 



sa, cell colony of many hundreds of protoplasts im- Slimy growths 



nosa 



bedded in a jelly-like suhstauce; x, single cells illustrating 

 division by fission 



or stones, wood- 

 work, and other objects, but certain types float freely in the 

 water in small' groups, or sometimes in large cell colonies. The 

 following types are representative. 



Glwocapsa i (Fig. 173, A) consists of cells with peculiar soft 

 walls which form concentric envelopes around the groups of 

 protoplasts. It is evident that the wall of each protoplast per- 

 sists for a long time after every cell division, so that groups of 



1 Chroijcoccus is an excellent substitute for Glceocapsa, and is not uncom- 

 mon in stagnant pools and on wet clay banks. Its cells are solitary and lack 

 the gelatinous envelopes of Gloeocapsa. 



