Smith—The Organization of the Colony . 
1189 
Petri dish cultures were used to determine whether these dif¬ 
ferent types of coenobe would give rise to the same type of coen- 
obe. Here each colony in the agar medium is the descendant of a 
single coenobium and microscopical examination shows that the 
two common types of coenobium are always present. The alter** 
nate arrangement is most noticeable in Scenedesmus acutus, al¬ 
though found in S. obtusus Meyen and S. quadricauda . I have 
also obtained S. obtusus in pure culture and find that Collins 
(15) is perfectly justified when he says that the variety alter 
nans (Reinsch) Hansg. of this species is “merely a form, hardly 
worthy of a name.” In 8 . quadricauda the alternate arrange¬ 
ment of the cells is the least pronounced of the three species 
studied. 
That a change in the composition of the nutrient medium 
does not affect the general arrangement of the cells in the coeno¬ 
be, although it may affect the individual cells, has been shown 
by Beyerinck (5) and more fully discussed by Serin (35). Col¬ 
onies grown in 0.1 per cent and 1.0 per cent Knop’s solution 
show both the linear and the alternate arrangement of the cells 
but there is a marked difference in the shape of the individual 
cells. (Compare Text figures 7 A and 7 B). When certain or¬ 
ganic compounds, as glycerine or glucose, are added to the nutri¬ 
ent solution there is a marked abnormal development of the 
individual cells, and a consequent abnormal appearance of the 
coenobe, but the fundamental axial relationships remain the 
same. Many of the abnormalities occurring under these con¬ 
ditions have been figured by Chodat (9). To; explain them he 
says that (p. 92), “the greater part of the forms obtained are 
accidental, that is they are the result of an unequal growth pro¬ 
duced by premature germination of the autospore within the 
interior of the mother cell.” Livingston (25) (26) (27) (28) 
(29) studied the cause which produces a change from the fila¬ 
mentous condition of Stigeoclonium to the “Palmella” condi¬ 
tion, where the cells are approximately spherical instead of be¬ 
ing cylindrical. In his earlier studies he considered osmotic 
pressure to be the sole controlling factor, since when the osmotic 
pressure of the medium is above a certain point the cells change 
