174 



THE ALGJE 



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

 esting fact that representative algse of these four classes can 

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



A 



CLASS I. THE BLUE-GREEN ALG.E, OR 

 CYANOPHYCEJ3 



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- 

 green algae. 



These forms 

 may develop as 

 slimy growths 

 on the surface 

 of 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. 



Glceocapsa 1 (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 



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

 cell colonies 



A, Glceocapsa, solitary cell and small groups held together 

 by the thick gelatinous envelopes ; B, Clathrocystis serugi- 

 nosa, cell colony of many hundreds of protoplasts im- 

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

 division by fission 



1 Chroococcus 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 Glceocapsa. 



