152 UNIVERSITY OF ILLINOIS 



dried in an oven, then I moistened with rain water and pressed hard 

 into it a shoot of willow weighing five pounds. After exactly five 

 years, the tree that had grown up weighed 169 pounds and about 

 three ounces. But the vessel had never received anything but rain 

 water or distilled water to moisten the soil, when this was necessary, 

 and it remained full of soil which was still tightly packed, and lest 

 any dust from outside should get into the soil, it was covered with a 

 sheet of iron coated with tin, but perforated with many holes. I did 

 not take the weight of the leaves that fell in the autumn. In the end 

 I dried the soil once more and got the same two hundred pounds that 

 I started with, less about two ounces. Therefore, the 164 pounds of 

 wood, bark and root, arose from the water alone." A notable con- 

 tribution, but only a part of the truth was found. 



Glauber believed that "saltpeter" contained these important 

 "principles." Kulbel was convinced of their presence in "humus." 

 Along about the middle of the sixteenth century, Tull wrote interest- 

 ingly of how plants feed. "It is agreed," he wrote, "that all the fol- 

 lowing materials contribute in some manner to the increase of plants, 

 but it is disputed which of them is that very increase of food : ( 1 ) 

 Niter, (2) Water, (3) Air, (4) Fire, (5) Earth." "Altho niter, 

 water, air, and fire and heat aid plants in growing, the earth is the 

 real food and increase of plants; niter and other salts prepare the 

 earth by dividing its particles, as a knife is to cut and prepare the 

 food ; water and air move it, and by carrying and fermenting it in the 

 juices of the plant to produce heat. Too much niter corrodes a plant, 

 too much water drowns it, too much air dries the roots, too much 

 heat burns it; but too much earth a plant can never have, unless it 

 be therein wholly covered up." Tull's work closes the period known 

 as the epoch of a search for the "principle of vegetation." 



EARLY EFFORTS TO ASCERTAIN "PLANT NUTRIENTS" 



According to Russel, the year 1750 marks the beginning of the 

 epoch regarded as a search for "plant nutrients." It was about 1755 

 when Home was set to work by the Edinburg Society "to try how 

 far chemistry will go in settling the principles of agriculture." Home 

 seemed to think that the whole art of agriculture centered in the 

 "nourishing of plants." His chief contribution to plant culture was 

 the emphasis he placed on a study of the function of "plant nutrients." 



Priestley, in 1771, pointed to the fact "that plants instead of af- 

 fecting the air in the same manner as animal respiration, reverse the 

 effects of breathing and tend to keep the atmosphere pure and whole- 



