Highly Organized Flora of Running Streams. 15 



composed of zoogloa masses of bacilli covering the sur- 

 face of the filtering bed and restrain the passage of all 

 organic matter, both living and dead, and break it up 

 into inorganic salts. 



The relation of these lower forms of micro-organisms, 

 all of which are chlorophyl-free, to the chlorophyl-bearing 

 organisms found in running streams is a most important 

 one. Through their operation the organic impurities are 

 broken up and mineralized, so that in turn they can again 

 serve as food material for the chlorophyl-bearing organisms. 

 The relation of these two groups of organisms in running 

 streams is similar to that of these organisms when found 

 in the soil and elsewhere. There is no doubt that were 

 all of the chlorophyl-free organisms to be removed from 

 the face of the earth, the life history of higher vegetation 

 would be a comparatively brief one ; being dependent 

 upon the continuous supply of the mineral salts capable 

 of serving as food material upon the activity of the 

 chlorophyl-free organisms. As soon as all of this avail- 

 able food material would be used up their life history 

 would be completed, and in turn the animal world would 

 be brought to the same termination as soon as all vegetable 

 life had ceased. 



