Smith—The Organization of the Colony . 1179 
in their arrangement when they come to rest. In Scenedesmns 
and Tetradesmus there is a very slight movement of th© auto- 
spores duei to their elongation. Those of Tetracoccus and 
Coelastrum do not move but round up and develop into mature 
cells in situ. For this reason the manner of cleavage in Tetra¬ 
coccus and Coelastrum is the chief factor determining the shape 
of the adult colony. 
At times the cells of the coenobe are arranged, not in the 
form of a more or less hollow sphere, but in that of irregular 
plates (Fig*. 4), or in an irregular, somewhat branching plate¬ 
like mass (Fig. 17). Strictly speaking the cells, in such a 
case, do not lie in a plane like those of Pediastrum, but consti¬ 
tute a partially flattened mass some of whose cells are above or 
below the others. Such a condition suggests that, in making 
a mount of the Coelastrum material, the pressure of the cover- 
glass may have crushed and flattened a coenobe of regular form. 
I do not believe this to have been the case, since I have observed 
these flattened masses in material that was carefully lifted from 
the culture by means of a platinum loop and then examined in 
a hanging drop. In some of these irregular cell masses there 
has plainly been a rupture of the tender gelationous processes 
that ordinarily hold the cells of the coenobe together (Fig. 17) ; 
in others (Fig. 4) the remains of such processes cannot be seen. 
There are two possible explanations for these variations from 
the ordinary arrangement of the cells of the coenobe. In 
Stigeoclonium Livingston (25) (26) (27) (28) (29), investi¬ 
gating the cause of the change from the filamentous to the “Pal¬ 
in ella” condition, finds that it may be due to an increased os¬ 
motic pressure of the nutrient solution, or that it may be in¬ 
duced by the toxic action of certain compounds, either organic 
(as bog extracts) or inorganic (as copper salts). The change 
in the arrangement of the cells of Scenedesmns acutus from a 
symmetrical coenobe with the cells all in one plane to an in¬ 
definitely branching system, which has been called the “Dactyl- 
OGoecus stage” by Grintzesco (17), might well be cited as an¬ 
other instance of this kind, but I wall show in the discussion of 
