investigation, and we are greatly indebted to him for summarizing 

 previous work and pointing out valuable lines of future research. 

 In his book (1840) he states, that 



a rational system of agriculture cannot be formed without the application 

 of scientific principles, for such a system must be based on an exact ac- 

 quaintance with the means of nutrition of vegetables, and with the influence 

 of soils, and actions of manures upon them. This knowledge we must seek 

 from chemistry, which teaches the mode of investigating- the composition and 

 study of the character of the different substances from which plants derive 

 their nourishment. 



In one essential point, however, he fell into error. Lawes, the 

 pioneer experimenter on agriculture in England, flatly denied the 

 accuracy of Liebig's conclusions as regards nitrogen assimilation. 

 The results of the investigations at Rothamsted as conducted by 

 Lawes and Gilbert (1851) on the non-assimilation of atmospheric 

 nitrogen by crops, were accepted as conclusive evidence upon this 

 much discussed question. 



The alkali soluble portion of the organic matter of the soil 

 has formed for many years the subject of keen interest and discus- 

 sion. This portion of the soil organic matter was called "humus" 

 by the earlier writers, but this name has in more recent times been 

 used by some American and most European investigators to desig- 

 nate the total organic matter of the soil. I have used the term 

 throughout this paper in its original meaning. In early days the 

 "humus" was regarded as being of very simple composition. De 

 Saussure (1804) for instance, described it as a "brown combustible 

 powder soluble in alkalies and ammonia compounds." 



Klaproth* applied the name "ulmin" to dark colored amorphous 

 bodies such as those obtained by Vauquelin (1797) from the bark 

 of diseased elm trees. Sprengel (De Candolle** 1833, p. 280), who 

 obtained similar bodies from soils applied to these the name "humic 

 acid." Berzelius (1838) evidently had the general meaning of the 

 term "humus" in mind when he used the term "humin" in describ- 

 ing certain dark colored constituents of vegetable mold. Follow- 

 ing the use of the term "humin" as applied to what was considered 

 to be a definite organic body, a number of other workers took up 

 the study of similar substances, and a number of other terms more 

 or less related, soon appeared. The name of Mulder (1849) is asso- 

 ciated for the most part with the terms applied to humus-like sub- 

 stances which have appeared more or less in the literature from that 

 time to the present. For instance, he says : 



At present seven different organic substances are known to exist in the 

 soil. They are crenic acid, apocrenic acid, geic acid, humic acid, and humin, 

 nlmic acid and ulmin. 



These bodies were divided by him into two groups, one con- 

 sisting of crenic and apocrenic acids, and the other group embrac- 

 ing all the others. According to Mulder (1849) these seven or- 

 ganic bodies were intimately related, and five at least were five suc- 

 cessive steps in the decay of organic matter in the soil. The first 

 step in this decay he regarded as ulmic acid ; this on further 

 oxidation yielded humic acid ; and this in its turn, on still further 

 oxidation, geic acid. Continued oxidation produced apocrenic, 

 and finally crenic acid. 



*(De Candolle 1833, p. 279) states "Das Ulmin ist von Klaproth entdeckt 

 ivorben." 



** I" have been unable to verify the original citation, which, according to 

 Uoper was Kastner's Archiv. Bd. 7, p. 163; Bd. 8, p. 145. Presumably one of 

 these articles is that referred to by Russell (1912) entitled "Ueber Pflanzen- 

 Xaturlehre, Niirnberg, 1826. 



