Smith—The Organization of the Colony . 1185 
the cel]ular arrangement of Pediastrum . He believes that all 
swarm-spores are morphogenetically equivalent; and that the dev¬ 
elopment of the horns is determined by cellular interaction. The 
arrangement of the cells in the form of a symmetrical coenobe 
results when the swarm-spores possess the normal motility; hut 
when the vitality of the swarm-spores is diminished, as in old 
cultures in which the general vitality of the alga is lowered, or 
in cases where the motility of the swarm-spores is hindered by 
unfavorable conditions, such as the lack of water on an agar 
slant, the swarm-spores do not reach a regular symmetrical ar¬ 
rangement before they cease moving, the result being the forma¬ 
tion of an irregular colony. Practically all deviations from 
the normal, in the arrangement of the cells, may be accounted 
for by the failure of the swarm-spores to assume the regular ar¬ 
rangement before the completion of the period of swarming. 
Scenedmmus, A Parallel Nonconctjrrent Colony 
Scenddesmus acutus . 
Several investigators have studied the effects of external con¬ 
ditions upon the shape of the colony and of the individual cells 
in this form. The species has been studied in pure culture by 
Beyerinck (5), Grintzesco (17), Chodat (9), Tischutkin (38), 
and Artari (3) ; and in unialgal culture by Chodat and Malines- 
Go (13) (14), Artari (4), and Senn (34). Chodat and Malin- 
esco describe a remarkable series of transformations. At one 
stage there are individual cells which resemble those of Pleuro- 
coccus, at other times of A nki&trodesmus (Raphidium), and at 
still other times branching systems of cells which resemble those 
of Naegeli’s Dactylococcus. This statement has been somewhat 
modified by Chodat (9) in a more recent publication, but not 
wholly abandoned. Senn (35) stated, as a result of his obser¬ 
vations, that Scenedesmus colonies could not be changed into 
other forms by varying the cultural conditions. When the alga 
was grown in water half saturated with carbon dioxid or oxygen 
the colonies separated into individual cells, but did not take on 
the chain-like arrangement of Dactylococcus. Nutritive solu- 
