CHAPTEE XVII 



THE GREAT GROUPS OF ALG^ 



158. General characters. — The Algae are distinguished 

 among Thallophytes by the presence of chlorophyll. It 

 was stated in a previous chapter that in three of the four 

 great groups another coloring matter is associated with the 

 chlorophyll, and that this fact is made the basis of a division 

 into Blue-green Algae (Cyanophyceae), Green Algae (Chloro- 

 phyceae), Brown Algae (Phaeophyceae), and Eed Algae (Rhodo- 

 phyceae). In our limited space it will be impossible to do 

 more than mention a few representatives of each group, 

 but they will serve to illustrate the prominent facts. 



1. Cyanophyce^ {Blue-gree7i Algce) 



159. Gloeocapsa. — These forms may be found forming 

 blue-green or olive-green patches on damp tree-trunks, rock, 

 walls, etc. By means of the microscope these patches are 

 seen to be composed of multitudes of spherical cells, each 

 representing a complete Glceocapsa body. One of the pecul- 

 iarities of the body is that the cell wall becomes mucilagi- 

 nous, swells, and forms a jelly-like matrix about the work- 

 ing cell. Each cell divides in the ordinary way, two new 

 Gloeocapsa individuals being formed, this method of vegeta- 

 tive multiplication being the only form of reproduction 

 (Fig. 201). 



When new cells are formed in this way the swollen 



mucilaginous walls are apt to hold them together, so that 



presently a number of cells or individuals are found lying 

 232 



