24 ALGM 



Respiration. Respiration or oxidation occurs as in all 

 living things. The exchange of gases between the organisms 

 and the surrounding medium is brought about by the differ- 

 ence in gas pressure. Since there is more carbon dioxide 

 within the organisms than without, therefore, the flow of 

 carbon dioxide is outward. In like manner, since there is 

 less oxygen within the cell than without, the flow of oxygen 

 is inward. 



FIG. 2. Nostoc. Numerous spherical and oblong masses or colonies com- 

 posed of thousands of filaments. 



Conclusion. Protococcus is irritable. Its wall consists 

 of cellulose, it has chlorophyll, it requires liquid or gaseous 

 food; therefore, it is a plant. 



NOSTOC 



Habitat. Nostoc is found growing in sluggish water and 

 on moist earth that is rich in decaying organic matter. 



