174 



THE ALG^E 



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

 esting fact that representative algre of these four classes can 

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



CLASS I. THE BLUE-GKEEN ALG.E, OE 

 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. 



. i / / //v.*'*ain//7.S'\\ \ \ 



A*3^A 



208. The one- 

 celled blue- 

 green algae. 



These forms 

 develop as 



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

 cell colonies 



A, Gloeocapsa, solitary cell and small groups held together 

 by the thick gelatinous envelopes ; B, Clathrocystis serugi- 

 nosa, cell colony of many hundreds of protoplasts im- slimy growths 

 bedded in a jelly-like substance ; x, single cells illustrating on j ie surface 

 division by fission 



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. 



Gloeocapsa 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 tune after every cell division, so that groups of 



1 Chroococcus is an excellent substitute for Gloeocapsa, and is not uncom- 

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

 the gelatinous envelopes of Glxocapsa. 



