soil, SESSION, 



153 



themselves and from the decay of organic matter disseminated among- 

 them. It is upon this surface that the soil organisms live which hasten 

 the decay of the organic matter and so charge the soil moisture with 

 plant food materials ; and it is against the same surface that the root 

 hairs of crops place themselves to appropriate both the moisture and 



nr 'THE 



PIHEST CLAY SOILS 

 WHERE 6000 ORAIHS, SIDE BY SIDE. MEA30BE ONE IMCH THERE ARE. 

 IB OHE CtTBIC FOOT, ABOOT 6 ACRES OF SOIL-GRAIN SURFACE. 



ONE CUBIC FOOT HAS ABOUT 7 ACHE OF SOIL-QBAIir SUEFACE; 



WHERE 1200 GRAINS. SIDE BY SIDE. MEASURE ONE INCH 

 ONE CUBIC FOOT HAS ABOUT ONE ACRE OF SOIL-GRAIN SURFACE. 



Fig. 2.— Showing by circles the relative diameters of the grains of coarse sandy soil ; 

 finest clay soil and loam soil, 636 times average diameter. 



what it has dissolved. The internal soil surface of every field is, 

 therefore, a pasture where plant food grows and upon which crops, 

 through their roots, feed. 



The extent of this internal surface is very great and very different 

 in the different soil types. Let me try to help you to better realize this 



