320 SOILS 



so completely controverts our generally accepted 

 beliefs unless there were abundant and weighty 

 evidence to prove that it is at least plausible. It 

 will be impossible to give here more than a bare 

 summary of the abundant evidence submitted in 

 support of the new theory. Briefly stated the main 

 lines of argument are: 



1. Practically all soils, including those that now 

 produce poor crops or are said to be worn out and 

 supposed to be exhausted of available plant food, 

 are really rich in available plant food. 



2. The cause of their unproductiveness, then, is 

 the condition of the soil, not its chemical content. 

 The problem of soil fertility is not concerned so 

 much with the amount of plant food in the soil as 

 with the condition of the soil. 



3. Plants excrete from their roots poisonous 

 substances which are to the plants what manure 

 is to animals the wastes. If the same kind of 

 plant is grown continuously on the same land, the 

 soil becomes so clogged with this plant manure that 

 this kind of plant will no longer thrive in it, but 

 other kinds of plants will. 



4. A water-culture of an unproductive soil an 

 exact duplication of the soil water in that soil 

 upon which plants feed will not grow plants 

 well until the impurities in it have been removed 

 with carbon black; after this is done plants 

 grow very vigorously in it. The chemical com- 

 position of the water-culture is the same as that of 

 the soil water of the unproductive soil in the field. 



5. Humus is Nature's carbon black. If an 

 abundance of humus is present in the soil it absorbs 

 these plant excrements and the soil is kept in a 

 sanitary condition. 



6. Commercial fertilisers are valuable not merely 



