SOILS AND FERTILIZERS 



INTRODUCTION 



PRIOR to 1800 but little was known of the sources 

 and importance of plant food. Manures had been 

 used from the earliest times, and their value was recog- 

 nized, although the fundamental principles underlying 

 their use were not understood. It was believed they 

 acted in some mysterious way. The alchemists had 

 advanced various views regarding them ; one was that 

 the so-called " spirits " left the decaying manure and 

 entered the plant, producing more vigorous growth. 

 As evidence, the worthless character of leached manure 

 was cited. It was thought the spirits had left such 

 manure. The terms 'spirits of hartshorn/ 'spirits of 

 niter,' ' spirits of turpentine,' and many others reflect 

 these ideas regarding the composition of matter. 



The alchemists held that one substance, as copper, 

 could be changed to another substance, as gold. Plants 

 were supposed to be water transmuted in some myste- 

 rious way directly into plant tissue. Van Helmont, in 

 the seventeenth century, attempted to prove this. " He 

 took a large earthen vessel and filled it with 200 

 pounds of dried earth. In it he planted a willow 



