206 TILLERS OF THE GROUND CHAP. 



What did Boussingault actually do? His object 

 was to grow plants from seed, giving them nothing 

 but water and air, and then find out if they con- 

 tained more or less nitrogen than was in the 

 original seed. If there was more in the little 

 plant than in the seed from which it grew, and the 

 plant t was given no nitrogenous manure, then it 

 must have taken this nitrogen from the air. In 

 other words, Boussingault wanted to answer the 

 question : Can a green plant take nitrogen from 

 the air ? 



He made in the first place a series of very 

 careful experiments, which seemed to show that 

 clover and peas can take nitrogen from the air 

 while wheat and oats cannot do this. He was not, 

 however, satisfied with these results, for he could 

 discover no reason why peas and clover should 

 differ so markedly from wheat and oats. He, 

 therefore, returned to his experiments again and 

 again, always endeavouring to make the conditions 

 more precise. For more than twenty years he 

 toiled over the question, and his final conclusion 

 was that plants cannot take free nitrogen from the 

 air. That is, he answered his own question in the 

 negative, believing that he had been misled in his 

 first experiments with clover and peas. 



A great number of other observers worked at the 

 same question, and with very varying results, some 



