Smith—The Organization of the Colony . 
1175 
and the spring of 1913. Drawings were not made at once, but 
the material was preserved in a 10 per cent solution of Am arm’s 
copper-lacto-phenol. 
The Isodiametric Series 
Although, from the morphological standpoint, the sphere is 
the simplest possible form that a cell may assume, this shape 
is found in but few cioenobie algae. This may be because the 
formation of autocolonies within the mother cell wall is a con¬ 
siderable advance over the condition of free-lying spherical cells, 
and because along with the development of this autocolonial 
habit there has gone almost necessarily an axial differentiation 
of the individual cells. It is true that certain of the Volvo- 
eales have symmetrical colonies composed of spherical cells but 
since these cells have a certain axial differentiation they have 
been excluded from consideration in this paper. Two coenobic 
algae with isodiametric cells are Tetracoecus botryoides West 
and Coelastrum microporum Xaeg. 
Tetracoecus, A Plane Isodiametric Colony 
In Tetracoecus botryoides West, which is taken as a type of 
coenobe whose cells lie in a single plane, my observations were 
made on material as it was collected from a small, sluggish 
stream near Madison, Wisconsin. 
There is little variation in the arrangement of the cells when 
they are found in a single plane. They may be arranged either 
so that the outline of the coenobe is rectangular (Fig. 1 A, 
Plate LXXXV) or so that it is diamond shaped (Fig. 1 B). This 
difference in outline depends upon the manner in which the cells 
of the coenobe come in contact -with one another; sometimes 
there is a small open space in the center of the colony (Fig. 1 
A), in which case the colony is rectangular in outline, some¬ 
times two opposite cells of the colony are in contact with one 
another, and the remaining pair of cells are not in contact but 
are prevented from touching each other by the first pair (Fig. 
