140 ARE SOILS ENRICHED, IMPOVERISHED, pt. hi. 



excretion, be the result of disease and decay or partial 

 maceration of the roots. There is no discoloration of 

 the water in which the seedlings of forest-trees are 

 made to grow, while these are in health. 



I imagine that trees, in absorbing by their roots the 

 moisture with which they come in contact, give off the 

 unnecessary parts of this by transpiration in the air. I 

 do not perceive what should cause roots to transpire 

 when surrounded by moisture ; or if they do, they must 

 return, like the dog to his vomit, and again absorb their 

 own transpirations. 



If it were owing to the poisonous excretions of the 

 roots that the same crops cannot be taken year after 

 year from the same land, this cause would apply 

 equally to all lands ; but there is an infinite variety in 

 soils in this respect. And this infinite variety, and the 

 infinite gradations in richness and productiveness of 

 different soils, prove that the nutriment of plants comes 

 from the soil, not from the air. Yet the very same 

 physiologist who makes the plant imbibe its food from 

 the air by its leaves, will force it to swallow poison 

 from the soil with its roots ! If plants feed through 

 the medium of their leaves from the air, why manure 

 the soil ? 



It is perhaps possible that the reason why each 

 plant appears to have its favourite soil is that it finds 

 there in the greatest abundance the particular inorganic 

 or incombustible matters adapted to its pecuhar consti- 

 tution ; that the reason why particular plants will not 



