136 



ARE SOILS ENRICHED, IMPOVERISHED, 



PART IIL 



AEE SOILS ENRICHED, IMPOVEKISHED, OR POISONED 

 BY VEGETABLE GROWTH? THESE QUESTIONS IN- 

 CLUDE EXCRETION FROM ROOTS; SOCIABILITY OF 

 PLANTS; ACCUMULATION OF SOIL IN WOODS; GENE- 

 RAL DENUDATION OF SOIL FROM WASH OF RAIN. 



The food of I THINK that tlie food of plants is absorbed from the 



plants is 



extracted soil, iiot froiii the atmosphere ; but that, if the remp^ins ' 

 it- the dead plants are restored to the soil from which they 



SurneT grew, owing to vegetable chemistry, independently of 



no impo- ' disintegration of rock, soils would become enriched, not 



verishment i t mi 



takes place impoverished. The two great causes of nnpo verishment 

 of soils are, abstraction of vegetable crops by man or 

 animals, and aqueous denudation, that is, the wash of 

 rain. The food of plants is of two sorts, the organic 

 or combustible^ that part which can be consumed in 

 burning ; and the inorganic or incombustible^ that part 

 which remains as ashes after burning. Both parts are, 

 in my opinion, absorbed by the roots from the soil ; at 

 least, what is absorbed as food from the atmosphere 

 may be reckoned as nothing in comparison to what is 

 absorbed by the roots from the soil. In reference to 

 the combustible constituents of the food of plants, 

 Liebig tells us that the presence of oxygen — conse- 

 quently, of atmospheric air — is necessary for the gene- 



