DEVELOPMENT OF ALGAE IN SOIL 



71 



TABLE 14 



Comparative Numbers and Weights of Cell Subst.^nce of Protozoa 



AND Bacteria in the Soil (from Cutler) 



face is controlled by factors similar to those which regulate the 

 distribution of other organisms, they are more numerous near the 

 surface, and have fewer species represented and less total number 

 of individuals in the deeper layers. Rarely do they appear in 

 abundance in soils of low water content. Grassland appears to 

 be a more favorable environment for their development than the 

 more highly cultivated soils. It has been estimated that, per 

 volume, they occupy about three times as much space per unit of 

 soil as the bacteria, and about one-third the space occupied by the 

 protozoa. Naturally they can hardly be present in such abun- 

 dance without exerting profound changes in certain soil processes. 

 According to Bristol-Roach, the actual numbers of algae in the 

 cultivated layers of agricultural soils range from 700 per gram to 

 many thousands, the numbers changing with depth of soil, season 

 of year, and soil treatment (Table 15). 



TABLE 15 



Influence of M.anure and Soil Depth upon the Distribution of Algae 



IN English Soils (from Bristol-Roach) 



