I. INTRODUCTION: OUR PRESENT KNOWLEDGE OF 

 THE ORGANIC MATTER OF THE SOIL. 



A. Early Investigations. 



It has been recognized from the time of the alchemists that 

 manures are of fundamental importance for the growth of plants. 

 The alchemists believed that by a process of transmutation water 

 was converted into plant tissue. In an attempt to prove this an 

 interesting experiment was conducted by van Helmont (1648). 

 In a large earthen vessel he placed 200 pounds of dry earth, and 

 planted in it a small willow tree weighing five pounds, and for five 

 years he watered the plant either with rain or distilled water. .At 

 the end of that time he pulled up the willow and found that it 

 weighed 169 pounds and three ounces. The dry soil remaining after 

 the experiment was found to have lost only two ounces. He drew 

 the apparently justifiable conclusion that 164 pounds of roots, bark, 

 leaves, and branches had been produced by direct transmutation 

 of water. 



It is evident that it was essential to establish the composition 

 of water and some of the components of the air before further 

 work could have real value. 



Not until the discovery of oxygen by Scheele (1777) and 

 the proof of the composition of water by Cavendish (1784), as well 

 as the work of de Saussure (1804) regarding the role played by 

 carbon dioxide in plant and animal life, did we have any real 

 knowledge concerning the sources of matter stored up in plants. 



During the first quarter of the nineteenth century organic com- 

 pounds were regarded as capable of being synthesized only in the 

 living cells of plants or animals. This idea that organic compounds 

 could be formed only through a special vital force was overthrown 

 by the classic work of Wohler (1828) when he prepared urea, a 

 purely animal product*, by evaporating ammonium cyanate to 

 dryness. This fact attracted the attention of chemists, and prac- 

 tically all work done from that time until 1840 was on some phase 

 of organic chemistry. This overthrow of the belief in a vital force 

 and the improved method of organic analysis by Berzelius (1808- 

 18) paved the way for a more thorough understanding of the part 

 taken by the organic matter in the soil, and consequently created 

 a renewed interest in scientific investigations relating to agricul- 

 ture. 



Some important work had been accomplished previous to this 

 time. The most valuable was that of de Saussure's (1804) "Re- 

 cherches chimiques sur la vegetation" which was the first syste- 

 matic work showing the source of compounds stored up in the 

 plant. He pointed out that the quantitative increase in the carbon, 

 hydrogen, and oxygen, when plants were exposed to sunlight, was 



*Fosse (1912) notes the presence of urea in certain plants. 



