ON THE FOOD OF PLANTS. 109 



u and azote, of which the first is essential to 

 " flame, and to the life of animals ; and that it 

 " likewise contains small quantities of aqueous 

 " vapour, and of carbonic acid gas : and Lavoi- 

 " sier proved that this last body is itself a com- 

 " pound elastic fluid, consisting of charcoal dis- 

 " solved in oxygene. 



" Jethro Tull, in his Treatise on Horsehoeing, 

 " published in 1733, advanced the opinion, that 

 " minute earthy particles supplied the whole 

 " nourishment of the vegetable world. That 

 " air and water were chiefly useful in producing 

 " these particles from the land ; and that ma- 

 " nures acted in no other way than in ameliorat- 

 " ing the texture of the soil : in short, that their 

 " agency was mechanical. This ingenious au- 

 " thor of the new system of agriculture, having 

 " observed the excellent effects produced in 

 " farming, by a minute division of the soil, and 

 " the pulverization of it, by exposure to dew 

 " and air, was misled by carrying his principles 

 " too far. Duhamel, in a work printed in 1754, 

 " adopted the opinion of Tull ; and stated, that 

 " by finely dividing the soil, any number of 

 " crops might be raised in succession from the 

 " same land. He attempted also to prove by 

 " direct experiments, that vegetables of every 

 " kind, were capable of being raised without 



