OF THE 



UNIVERSITY 



OF 



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 rec- 

 ognized, although the fundamental principles under- 

 lying their use were not understood. It was believed 

 that they acted in some mysterious way. The alche- 

 mists had advanced various views regarding their ac- 

 tion ; one was that the so-called " spirits " left the de- 

 caying manure and entered the plant, producing more 

 vigorous growth. As evidence, the worthless charac- 

 ter of leached manure was cited. It was thought that 

 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 com- 

 position of matter. 



The alchemists held that one substance, like copper, 

 could be changed to another substance, as gold. Plants 

 were supposed to be water transmuted in some mys- 

 terious 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 

 weighing 5 pounds, which he duly watered with rain 



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