INTRODUCTION 5 



work of Boussingault covered a variety of subjects re- 

 lating to plant growth. He repeated and verified 

 much of the earlier work of DeSaussure, and also 

 secured many additional facts relating to the chemis- 

 try of crop growth. As to the source of nitrogen in 

 crops, he states that : "The soil furnishes the crops 

 with mineral alkaline substances, provides them with 

 nitrogen, by ammonia and by nitrates, which are 

 formed in the soil at the expense of the nitrogenous 

 matters contained in diluvium, which is the basis of 

 vegetable earth ; compounds in which nitrogen exists 

 in stable combination, onlv becoming" fertilizing bv 

 the effect of time." As for the absorption of the gas- 

 eous nitrogen of the air by vegetable earth, he says : 

 " I am not acquainted with a single irreproachable ob- 

 servation that establishes it ; not only does the earth 

 not absorb gaseous nitrogen, but it gives it off." 2 



The investigations of DeSaussure and Boussingault, 

 and the writings of Davy, Thaer, Sprengel, and Schub- 

 ler prepared the way for the work and writings of 

 Liebig. In 1840 he published "Organic Chemistry 

 in its Applications to Agriculture and Physiology". 

 Liebig's agricultural investigations were preceded by 

 many valuable discoveries in organic chemistry, which 

 he applied directly in his interpretations of aoricul- 

 tural problems. His writings were of a forcible char- 

 acter and were extremely argumentative. They pro- 

 voked, as he intended, vigorous discussions upon 



