CONCERNING THE TEXTURE OF THE SOIL 



37 



way : it either never fructifies or does so in a feeble way 

 only. In the first case air was excluded, although much 

 moisture was present : enough to dissolve plant food and 

 carry it through the plant. In the second place, air was 

 free to enter, but so little moisture was present the plant 

 food was dissolved poorly and as poorly carried into the 

 plant. 



The pore-space of the soil. Both the air content and 

 the water content of the soil are governed and controlled 

 by the pore-space of the soil. Since the soil is composed 

 of particles of sand, silt, clay, and humus, and since these 

 vary in size and in numbers as well as in arrangement, 

 it follows that open spaces will naturally exist at the meet- 

 ing points of these many particles. It were impossible for 

 man or nature so to arrange these particles that no open 

 spaces might exist. Where the larger grains predomi- 

 nate, large open spaces naturally result, while where the 

 clay particles the 



LARGE PARTCLE. 

 LARGE PORE-SPACE 



SMALL PARTICLE. 

 SMALL PORE-SPACE 



finest grains pre- 

 dominate, the open 

 spaces are very tiny, 

 indeed. 



The number of 

 pores is less in the first 

 than in the second 

 instance, but, on the 

 other hand, they are 

 much larger. 



The diagram illustrates the idea. The pore spaces of 

 sand types are larger in size but smaller in number than 

 those of the clay types. 



The water films. When you pour water over a hand- 

 ful of marbles, you note that it runs off but leaves the 

 marbles wet. In other words, a film of water, surround- 



THE PORE-SPACE OF THE SOIL 



