28 



INTRODUCTION TO PLANT GEOGRAPHY 



[chap. 



Bacteria may dominate, and also, of course, in diseased or decaying 

 systems. They may also be the pioneers in the colonization of some 

 bare areas. 



Cyanophyceae : These are the so-called ' Blue-green Algae ', or 

 Schizophyceae, but they seem to have their closest relationship with 

 the Bacteria, which they resemble particularly in their lack of a 





^^^•^m^^ 





Fig. 4. — Various Blue-green Algae (Cyanophyceae). A, Riviilan'a ( ■: about 600) • 

 B, Aphanotfiece ( ' about 1500); C, Merisniopedia ( ■ about 200); D, Oscilloloria 

 ( ;< about 800); E, a species of Nostoc, consisting of filaments embedded in a 

 gelatinous matrix (x about 300); F, Gloeocapsa: a single-celled individual and 

 colonies of two, three, and four cells ( < 1285). 



typically organized nucleus in the cell, in their method of cell 

 division, and in the obscurity at all events of any sexual reproduction. 

 They consist either of single cells, of cells joined end-to-end to form 



