CHAPTEE XVII 
THE GREAT GROUPS OP ALG-EJ 
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-green Algae) 
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 Gloeocapsa 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 
