82 



CHEMISTRY OF FARM PRACTICE 



depths parts of the Mississippi basin. The loess deposits 

 extend from Illinois and Iowa as far south as some parts 

 of Mississippi. 



FIG. 29. Saprophytic plants called " frog stools " indicate that 

 decay has begun. (Farmers' Bulletin 468, U. H. Dept. Agr.) 



The gravity-moved soils are termed colluvial, and are 

 not very extensive. 



64. Gain and Loss of Plant Food. Two sets of factors 

 affect the fertility of soil, both of which may be modified 



