Smith—The Organization of the Colony. 1187 
In my experiments I have grown Scenedesmus acutus under 
a variety of conditions and have been able to cause the dissocia¬ 
tion of the cells of the coenobe, to some extent, but have never 
obtained a cellular arrangement resembling the Dactylococcus 
condition found by Grintzeseo. Cultures have been kept under 
observation for nine months and at the end of that time many 
plate-like colonies were present, and although some isolated cells 
appeared there was not the slightest tendency toward the forma¬ 
tion of chains of cells. 
On the other hand, an alga was also isolated in the summer 
of 1911 that gave beautiful chains of cells with the regular 
Dactylococcus infusionum arrangement. Photomicrographs of 
this alga are shown on Plate XOX. Changes in the cultural 
conditions of this alga cause a cessation of the chain formation 
and a breaking down into isolated cells, recalling the ‘'B,aphi- 
dium” stage of Grintzeseo (Pigs. 133 and 134). There is never 
a formation of plate-like colonies. A slight approach to this 
may be found at times where two or three cells lie side by side 
but these cannot be regarded as regular Scenedesmus acutus 
coenobes (Figs. 130, 134-136). Under certain conditions the 
arrangement of the cells in a polygonal meshwork suggests Hy- 
drodidyon (Figs. 138-141), but these polygons never form a 
closed net as do the cells of Hydrodidyon. As a result of the 
work of Grintzeseo, West (41), Oltmanns (33), and Wille 
(43), abandon the Dactylococcus infusionum of Xaegeli and 
treat it as merely a physiological stage of Scenedesmus acutus. 
My observations show that the two species are distinct, both of 
them having a constant form, and that one never gives rise to 
the other. 
Comparing the coenobia of Scenedesmus, in a culture con¬ 
taining only the descendants of a single colony, more or. less 
variation will be found. That the number of cells in a colony 
varies from 2 to 16 is well known. The earlier systematise, 
Kuetzing (23) for example, were inclined to consider the four 
and the eight-celled colonies as belonging to different species, 
but this view is no longer held. It is generally agreed that en¬ 
vironmental conditions cause this variation in the number of 
