THE BLUE-GEEEN ALG^ (CYANOPHYCE^) 185 



individual greatly exceeding its thickness. Some of them per- 

 form a peculiar swinging or oscillating movement, from which 

 the generic name Oscillatoria is taken. They may, however, 

 move forward as well as sidewise. 



Under a compound microscope OsciUuturia is seen to con- 

 sist of a great many cells held very closely together in a 

 common tubular sheath (Fig. 154). If free from the sheath, 

 one of the cells assumes the 

 spherical form. But normally 

 the cells are compressed so 

 closely in the sheath that the 

 separate walls appear as one 

 common wall. A plant there- 

 fore consists of many of these 

 cells held together in a common 

 wall. It may grow in length by 

 having the cells divide, which 

 they regularly do. 



As compared with Glceooapsa 

 and Nbstoc, Oseillatoria contains 

 a great deal of chlorophyll, 

 which may be much or little 

 obscured by blue coloring mat- 

 ter. It lives in water, often at 

 the outlets of sewers and drains, or upon damp surfaces, from 

 which it absorbs the needed materials for the construction of 

 foods. It grows vigorously, being able to thrive throughout 

 a wide range of temperature and other climatic conditions. 



170. Oseillatoria : reproduction. Division of cells in this plant 

 does not necessarily mean reproduction of the individual, but 

 may signify merely its growth. A single Oseillatoria cell may, 

 if free, grow until it has reproduced a plant similar to the one 

 from which it came. This is not, however, its usual method 

 of reproduction. In a long specimen usually one or more cells 

 die, thus weakening the sheath that holds the cells together. 

 This allows the plants to break at these points, and each piece 



Pio. 154. Oseillatoria 



A, tips of several plants; B, part of 



one plant enlarged to show cellular 



structure. Both magnified, B much 



more than A 



