CHAPTER II. 



ESSENTIALS OF PLANT LIFE. 



Prior to 1840, comparatively little was done to apply chemistry 

 to the solution of agricultural problems. Much information was 

 collected regarding the chemical composition of soils, plants, and 

 animals, and a few books discussing the i elation of chemistry to 

 agriculture were published, those of Sir Humphrey Davy and 

 Thaer being perhaps the most important, but the fundamental 

 principles of plant and animal nutrition were not recognized, and 

 the books offered little of practical importance to the farmer. 



At that time the prevailing theory was that plants feed upon 

 the organic matter, or humus, of the soil, just as animals feed on 

 organic matter. According to this theory, the soil should be kept 

 full of vegetable matter to feed the plant. The ash or mineral 

 matter of the plant, whose presence was known and could not be 

 ignored, was thought to act as a stimulant, and not as food. In- 

 deed, Thaer, and perhaps others, held that mineral matter could 

 be created by plants. 



The great German chemist, Justus von Liebig, in 1840 publish- 

 ed a little book entitled "Chemistry in its Application to Agricul- 

 ture and Physiology," which developed an entirely new theory of 

 plant nutrition. Plants, he said, do not secure their organic mat- 

 ter from the soil, but from the air. He showed by calculations 

 that there is not enough organic matter in the soil to produce 

 average yields of farm crops. The material of importance which 

 comes from the soil, he said, is the mineral matter. Supply the 

 soil with a sufficiency of mineral matter, and it will remain fertile, 

 regardless of its content of organic matter. Such, in brief, was 

 Liebig's mineral theory of plant nutrition. This was a practical 

 theory and easily tested. Liebig himself, as an object lesson, 

 transformed a barren, sandy piece of land near Giessen, Germany, 

 into a beautiful garden, by means of his mineral manures. Mr. 

 John Lawes was incited to begin field experiments at his manor 

 of Rothamsted, England. 



These experiments led to the discovery of the process of mak- 



