THE ALG 
217 
due to the pressure exerted upon each by its neighbors, 
since at the tips of the filaments and on each side of a 
dead cell the unopposed pressure of the protoplasm causes 
the cell-walls to become con- 
vex (see Sect. 280). 
Oscillatoria contains 
abundant coloring matter of 
a bright bluish green or steel 
blue. If a small quantity 
of dried Oseillatoria is pul- 
verized and then soaked in 
water, the water is colored 
blue by the pigment which 
it extracts from the cell- 
contents. The residue may 
then be treated with alcohol, 
which becomes green from 
the chlorophyll dissolved 
from the Oseillatoria. 
Photosynthesis is carried’ 
on readily by this plant, as 
is evident from the oxygen 
bubbles which it gives off 
freely in sunlight. 
Reproduction in Oseilla- 
toria is usually performed 
by the breaking off of fila- 
ments at the places where 
dead cells occur. Each sepa- 
Fig. 751g] Blue-Green Alga. 
A, a filament of Calothriz, reproducing 
by hormogonia, h, segmented portions 
which escape from the sheath of the 
filament; B, Rivularia. (Both A and 
B greatly magnified.) 
rated bit of filament continues to produce new cells by 
the formation of new partition walls (Fig. 152). 
The 
simple method of cell-division shown in the figure is not 
