1 14 SOILS 



atmosphere furnished nitrogen to the clover plant. So 

 spoke Ville : the free nitrogen of the atmosphere becomes 

 food for clover and for some other plants. 



But the difference was not explained, for at that time it 

 could not be explained. The time was still unripe. 



Enter the microscopic plant : soil assistants in nitrogen- 

 getting. Now comes Berthelot, a French investigator, 

 with the theory that in the soil there are great numbers 

 of microscopic plants, living in the soil and belonging to 

 the soil, in fact, being a part of the soil itself; that these 

 are useful and valuable plants, small though they may be ; 

 and that these tiny plants do this thing: they help the 

 soil secure atmospheric nitrogen, and help it in such a 

 way that all plants growing therein get the good of it. 

 And Berthelot was right so far as he went, for he started 

 in the direction in which the true explanation was later 

 found. 



The concluding theory : the secret of the root tubercle. 

 This entire mystery was cleared at last by Hellriegel and 

 Wilfarth, who found, by their investigations, that certain 

 plants, like cereals and grasses, within limits, grow in pro- 

 portion to the amount of plant food supplied including 

 nitrogen. If an abundance of mineral elements and nitro- 

 gen was supplied the soil, there was secured always a 

 most bountiful harvest; if, on the other hand, nitrogen, 

 for instance, was withheld, a feeble growth, only, re- 

 sulted, if, indeed, a lingering death did not actually take 

 place. 



With the legumes clover, lupines, peas, beans, etc. a 

 different behavior was observed. Instead of dying, when 

 the nitrogen content was consumed, these plants recov- 

 ered, very rapidly, indeed, and until maturity, maintained 

 a most luxurious growth. And this condition prevailed 

 despite the fact that no nitrogen compound of any sort 



