Smith—The Organization of the Colony . 
1169 
B—Eonconcurrent forms. 
a—Parallel colonies: Scenedesmus acutus Meyen. 
b—Ebnparallel colonies: Crucigenia rectangularis 
(Eaeg.) Gay. - 
2—Eoncoplanar series. 
A—Concurrent forms. 
B—Eon concurrent forms. 
a—“Parallel colonies; Tetradesmus wisconsinensis 
Smith. 
b—-Eonparallel colonies. 
Figure 6. Possible combinations of the four cells of a coenobe in a nonparallel 
nonconcurrent noncoplanar series. Shaded diagrams represent those ar¬ 
rangements which are known to exist in nature. 
In the present paper a form from each of the main classes 
will be taken up and discussed both with respect to the varia¬ 
tions that normally occur in the coenobe, and to the modifica¬ 
tions that can be produced in the cellular arrangement by altered 
environmental conditions. 
