Smith—The Organization of the Colony . 
1193 
Either on account of the lack of this material, or on account of 
a rupture of it during the liberation of the young coenobe, in 
certain colonies the cells are not completely united but there 
may be two halves of the coenobe that are only partly joined 
(Fig. 45). At other times the two halves of the coenobe may 
be completely united but these halves are at an angle with 
each other (Fig. 97). 
Briefly summarizing the causes for the variations occurring 
in the cellular arrangement of the four cells of Scenedesmm 
acuius we may catalogue them in the following manner: 
I. formal Variations. 
Variation in the elongation of the daughter cells caus¬ 
ing either the linear or alternate type of coenobe. 
II. Abnormal Variations. 
1. Cellular monstrosities. 
2. Irregularities in the formation of the second clevage 
planes. 
A. Formation of cleavage planes in unusual 
directions. 
Bi. Incomplete formation of cleavage planes. 
0. Failure to form second cleavage planes. 
3. Irregularities occurring in liberation of young 
colonies. 
A. Failure of colony to unroll completely and a 
resultant curved colony. 
B. Partial fragmentation of colony during liber¬ 
ation. 
I 
Scenedesmus quadricauda. 
There is the same normal variation in the arrangement of the 
cells of the coenobe of Scenedesmus quadricauda that there is 
in the coenobe of S. acutus, although in the former the linear 
type of colony is much more abundant that the alternate type. 
The alternating character of the cellular arrangement is not 
so sharply marked as is the case in S. acidus. In another con¬ 
nection I have pointed out that there is a difference between 
