THE ALG.E 



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 Oscillatoria 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 Oscillatoria. 



Photosynthesis is carried 

 on readily by this plant, as 

 is evident from the oxygen 

 bubbles which it gives off 

 freely in sunlight. 



Reproduction in Oscilla- 

 toria is usually performed •^. ^ filament of Calothnx, reproducing- 



by/tomiojronia, A, segmented portions- 

 by the breaking on of lila- which escape Irom the sheath of the 

 mentS at the places where filament; 5, ffi^aiaria. (Both ^ and 

 '^ £ greatly magnified.) 



dead cells occur. Ji/ach sepa- 

 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 



Pig. 151. Blue-Green Algae. 



