During the last ten years a large number of organic compounds have been isolated from soils by Schreiner and his coworkers, Shorey, Walters, Lathrop, and Wise, of the Laboratory of Soil Fertility Investigations . Previous to that time the constituents of the organic matter of soils were practically unknown . The individual compounds isolated are agroceric acid (46), agrosterol (46), arginine (49), acrylic acid (61), adenine (61), benzoic acid (62),a-crotonic acid (82),creatinine (6o), cyanuric acid (85), choline ((1), cytosine (49), dihydroxystearic acid (46, 48), glycerides (49), guanine (42), hentriacontane (49), histidine (49), hypoxanthine (49), lignoceric acid (49), lysine (61), monohydroxystearic acid (49), metahydroxytoluic acid (62), mannite (61), nucleic acid (61), paraffinic acid (49), peptones (81), proteoses (81), pentosan (49), pentose (49), phytosterol (49), picoline carboxylic acid (47, 48), oxalic acid (6r ), rhamnose (61), resin (49), resin acids (49), resin esters (49), saccharic acid (61), salicylic aldehyde (61), succinic acid (6r), sulphur (61), trimethylamine (61), tetracarbonimid (63), trithiobenzaldehyde (6r), vanillin (62), and xanthine (49) .
From this list it is seen that the compounds represent a great variety of chemical classes : there are paraflinic hydrocarbons, hydroxy fatty acids, and other organic acids, organic bases, esters, alcohols, aldehydes, carbohydrates, hexone bases, pyrimidine derivatives, purinc bases, pyridine derivatives, organic sulphur compounds, organic phosphorous compounds, and nitrogenous compounds .
Especially interesting, in passing, are the groups of nitrogenous compounds .
Some of these are beneficial and others harmful to plant growth ; they are absorbed by plants as such, enter into the cell, and react with the protoplasm, causing effects either beneficial or detrimental, as the case may be . Among the beneficial compounds of this class which have been found in soils are creatinine (64, 65), creatine (64, 65, 1o), hypoxanthine (54, 56) . xanthine (54, 56), nucleic acid (54, 56), guanine (54, ro), histidine (54, 66), arginine, (54, 66), and choline (J4) . Other nitrogenous compounds reported as beneficial are acetamide (25), alanine (54, 25, 24, 31, io), allantoin (54, 31), amygdaline (31), asparagine (54, 31, 24, 1o), betaine (30), formamide (25), glycocoll (54, 25, 24, 31), and leucine ( ;4, 31) .
Not all nitrogenous compounds are beneficial, as is shown by