INTRODUCTION 



13 



truth to those of Nature, but teaches orderly mental 

 processes, which greatly aid in searches for light. 



A recent apparent conflict of academic knowledge 

 with field practice will illustrate : Soils from worn 

 out potato fields examined in the laboratory were 

 found to contain abundant food of all forms neces- 

 sary to grow potatoes. There was sufficient matter 

 therein, both organic and inorganic, to supply usual 

 quantities for normal growth, but notwithstanding 

 good tilth was maintained, the fields failed to pro- 

 duce crops. This was an opportunity to decry that 

 science was wrong in determining that such plant 

 food existed in the soil at all ; but when the chemists 

 looked further it was found the excreta from potato 

 vines was toxic, and finally accumulated in the soil 

 sufficiently to poison the roots ; that the ground re- 

 quired renovation by the growth of other vegeta- 

 tion, or recuperation by summer fallowing. 



Whether applied to tillage of fig trees or to other 

 horticultural lines, a knowledge of plant nutrition, 

 soil chemistry, wood and fruit formation, and dis- 

 eases of trees, called scientific agriculture, forms 

 only a basis of information for field work. Even 

 the broadest knowledge of statistics about farm 

 practices will often mislead, unless applied with 

 discriminating care, following faithfully our pri- 

 mary rules of botany, physics and chemistry. There 

 was an occasion, recently, to investigate the use of 

 field peas for soil renovation, and from considerable 



