November 1, 1912] 



SCIENCE 



581 



soil extract and the growth is now even 

 better than in the distilled water. 



Another experiment with soil and car- 

 bon black was made as follows : A layer of 

 moist carbon black was covered with a 

 layer of moist unproductive soil and this 

 in turn by a layer of moist carbon black. 

 In this experiment the moisture could cir- 

 culate from the soil to the carbon black 

 and back again and thus gradually the soil 

 fluid would be freed of any injurious com- 

 pounds by absorption into the carbon 

 black. At the end of a day or two of this 

 interaction the soil was freed from the 

 carbon layers, plants were grown in it, and 

 when compared with soil not so treated a 

 very marked improvement was shown, 

 again indicating that a harmful body was 

 originally present and had been removed 

 in whole or in part by this carbon black 

 treatment. 



Observations of this kind on many soils, 

 together with a study of the properties of 

 the material dissolved in the water, led to 

 no definite isolation of the compound or 

 compounds showing the harmful effect, 

 owing to the fact that the quantities in 

 the water extract are too small for identifi- 

 cation, but they did lead to a recognition 

 that the substances were not mineral in 

 character, but were constituents of the 

 organic matter of the soils. 



That organic substances could produce 

 such effects in such small quantities as 

 must be present in soil solutions was not 

 apparent from the literature and it be- 

 came necessary to establish this point. 

 With this in view, a test of about forty 

 substances of organic origin which may 

 get into the soil or be formed therein were 

 tested, and it was conclusively shown that 

 a number of these were decidedly harmful 

 to plants, even in very dilute solutions 

 comparable with the organic content of 

 soil solutions. 



It therefore became essential to make a 

 study of the organic matter of the soil. 

 The organic matter of the soil, however, 

 was a subject about which the older chem- 

 istry of agriculture had much to say, but 

 in regard to which modern science was 

 discreetly silent. With no established 

 facts and no methods of attack worked 

 out, progress was necessarily slow at first, 

 but gained speed with each compound iso- 

 lated or identified until to-day there have 

 been isolated in these laboratories more 

 than twenty-five definite compounds from 

 soil organic matter and the work is pro- 

 gressing at a rapid pace. 



The search for this supposedly harmful 

 constituent was rewarded by the discovery, 

 among others, of dihydroxystearic acid, a 

 compound which, on account of its fre- 

 quent occurrence in soils, has been rather 

 thoroughly studied in regard to its effect 

 on plant development and growth. 



The isolated and purified dihydroxy- 

 stearic acid was tested by dissolving it in 

 pure distilled water and it was found to 

 have decided deleterious action on the 

 wheat seedlings used in the tests. The 

 acid prepared in the laboratory behaved 

 in the same manner. 



Its effect in the presence of nutrient 

 salts was also extensively stiidied in solu- 

 tions containing calcium acid phosphate, 

 sodium nitrate and potassium sulphate, 

 alone and in combinations of two and three 

 of these salts, a total of sixty-six cultures 

 being used in a single test. The injurious 

 effect of the dihydroxystearic acid was less 

 where all three of the nutrient elements 

 were present than where only one or two 

 were present. The injurious effect was 

 least in those cultures of three nutrients 

 where the nitrate was high. This indicates 

 that the action of the nitrate tends espe- 

 cially to overcome the harmful effect of the 



