THE WORK OF ROOTS 



127 



shading (the dots are not intended to represent indi- 

 vidual soil-particles or aggregations) . At ( s ) is the 

 surface-crust, which may become very hard by the 

 baking of the sun and the beating of rain upon it, as 

 well as by the deposit of salts which are left behind as 

 the water evaporates. In soils where such salts are 

 very abundant (alkali soils) they form a whitish deposit 

 on the surface. This action of salts may be very 

 clearly illustrated by placing a little strong eosin solu- 

 tion or a little table salt in the bottom of a tumbler 

 and then filling the tumbler w T ith wet sand and allow- 

 ing it to stand in the sun for a few days. 



As we go deeper the soil becomes less compact (as 

 indicated in the figure) until a certain depth is reached, 

 when it begins to grow more compact as the subsoil is 

 approached. 



The plow removes a slice of soil and inverts it; 

 in ideal plowing the in- 

 verted portion (called the 

 furrow slice, fs) is left in 

 a loose, friable condition. 

 On examining it, we find 

 it broken up into small 

 rounded masses (soil- 



crumbs , Or floCCUles) , aS 

 i -nv rvo in i 



shown in Fig. 93. Each 



one of these masses is made up of a number of small 



soil-particles, as shown in Fig. 94, which repre- 



93. Part of furrow slice (of Fig. 92) magnified 

 to show floccules, or soil-crumbs. 



