2 MANURES FOR FRUIT TREES 



Virgil, Pliny, Varro and Columella were authors 

 who wrote upon manures and the art of manuring 

 in the early days of the world's history ; and 

 although the cultivation of the soil occupied the 

 attention of the ancients, agricultural chemistry 

 is a science of modern growth. The sources of 

 plant foods were found to be the atmosphere and 

 the soil. The composition of the atmosphere was 

 not discovered until the close of the eighteenth 

 century,^ and the chemistry, bacteriology and 

 physics of the soil are questions which still require 

 much research and patient investigation, although 

 great progress has been made during the past 

 few years in the elucidation of the subjects. 



Van Helmont's Theory. — One of the 

 earliest theories concerning the growth of trees 

 was that of the alchemist Van Helmont (1577- 

 1644). He believed that their food was water. 



Digby's Theory.— Sir Kenelm Digby (1660) 

 believed that plant growth was due to a balsam 

 contained in the atmosphere. He laid special 

 stress upon the virtues of saltpetre as a manure 

 for rose-trees, barley and hemp, but asserted that 

 saltpetre acted like a magnet, and attracted from 

 the air "a hidden food of life." 



1 Further discoveries were made a few years ago by Rayleigh 

 and Ramsay. 



