CIIAPTEE XVII 



THE GREAT GROUPS OF ALG^ 



158. General characters. — The Algas are distinguisliecl 

 among Thallopliytes by the presence of chloropliyll. It 

 was stated in a previous chapter that in tliree 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 Alggg (C'yanojihyceaj), Green Algaj (Chloro- 

 phyceffi), Brown A\g-x (Phajophyeea?), and Red Alga? (Rhodo- 

 phycese). In our limited space it will be imjDOssible to do 

 more than mention a few representatives of each group, 

 but they will serve to illustrate the prominent facts. 



1. CyANOPiiYCE.E {Blv.e-(jreen Alga') 



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 microscoj^e these patches are 

 seen to be composed of multitudes of spherical cells, each 

 representing a complete Glu'dcnpsd 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 

 Gl(i'(ic(vpxa individuals l)eiug formed, this method of vegeta- 

 tive multii^lication being the only form of reproduction 

 (Fig. 201). 



When new cells are formed in this way the swollen 

 mucilaginous walls are apt to liold them together, so that 

 p)resently a number of cells or individuals arc found lying 



