Smith—The Organization of the Colony . 1199 
The variations occurring in the position of the cells in the 
coenobe correspond to the linear and alternate arrangement in 
the Scenedesmus colony. A plane passed through the ends of 
all of the cells is at right angles, (Fig. 125), or at an angle 
(Fig. 118), to the long axis of the coenobe. This variation 
in the arrangement of the cells is due to the same sort of vari¬ 
ation in cleavage that oecurrs in Scenedesmus acutus. 
In connection with the description of Tetradesmus (36) the 
statement was made that there was always four cells present. 
A very few cases have since been found of two- and three- 
celled colonies. The formation of the two-celled colony is due 
to the elimination of one series of cleavages. Figure 122 
shows that there may also be a rotation of one of the daughter 
cells through an arc of 90 degrees. To explain such a change 
we must assume a change in the polarity of the daughter cell 
before the elongation takes place. 
Certain other abnormalities are connected with the liberation 
of the young colony from the old mother cell wall. One might 
expect that some of the colonies would unroll and take the form 
characteristic of Scenedesmus but this has never been found. 
The cells are ordinarily attached along the middle third of 
their length (Fig. 119) but sometimes the attachment is in the 
terminal third and the rest of the cell lie free (Fig. 124). 
Such an arrangement may be due to an arresting of the libera¬ 
tion of the young coenobe and a pressing together of the por¬ 
tion of the colony that has not been liberated. Eventually 
the colony becomes free but the unusual cellular arrangement 
persists. 
Discussion. 
The study of the variations occurring within the limits of 
any particular species naturally leads to a discussion of the 
doctrine of polymorphism. The historical side of the question 
has been thoroughly reviewed by both Grintzesco (17) and 
Chodat (9) and reference may be made to the work of these 
authors. The earlier view, expressed by Kiitzing (24), that 
there could be a change in algae as great as a passage from one 
