322 EXPEEIMENT STATION RECORD. [Vol.38 



tion of the content of colloidal clay In the foregoing manner in the case of 16 

 Leeward Islands soils are appended. 



The proof of microbial agency in the chemical transformation of soil, H. J. 

 Conn {Science, n. ser., 46 {1917), No. 1185, pp. 252-255) .—The author is of the 

 opinion that " to show conclusively the agency of any microorganism in any 

 chemical transformation occurring in soil, the following steps are necessary : 

 (1) The organism must he shown to be present in active form when the chem- 

 ical transformation under investigation is taking place, (2) it must be shown 

 to occur in larger numbers under such conditions than in the same soil in which 

 the chemical change is not occurring, (3) it must be isolated from the soil and 

 studied in pure culture, and (4) the same chemical change must be produced 

 by the organism in experimentally inoculated soil, making the test, if possible, 

 in unsterilized soil." 



[Soil bacteriology], C. M. Hutchinson {Ann. Rpt. Bd. Sci. Advice India, 

 1915-16, pp. 114-116). — In studies of soil toxins and nitrification "a series of 

 field experimental plats under wheat demonstrated the production of infertility 

 in soil containing nitrogenous organic matter (oil cake) as a consequence of 

 semianaerobic conditions artificially induced by water-logging. This infertility 

 did not occur to the same extent when ammonium sulphate was substituted fpr 

 cake, nor did the effect of the water-logging become apparent until the roots 

 of the plants had gone down some inches, to that level in the soil which oxida- 

 tion consequent on the cultivation had failed to reach. Parallel plats with bar- 

 ley illustrated this effect more markedly than those with wheat. . . . Labo- 

 ratory work on nitrification and on the growth of seedlings in water and soil 

 cultures demonstrated the possibility of separating substances from certain 

 bacterial cultures, from decomposing organic matter, and from anaerobically 

 incubated soil whose toxicity to nitrifiers. and in greater concentration to seed- 

 ling plants, was demonstrable under these conditions. 



" Observations were made as to the interference with the growth of seedlings 

 resulting from the bacterial invasion of the unexhausted and still attached 

 seed and the consequent absorption by the plant of toxic bacterial by-products. 

 This invasion occurred most readily in water-logged soil and more especially 

 in the presence of the bacteria derived from anaerobically incubated soils of 

 high organic matter content. Copper sulphate was found to neutralize most 

 of the toxic bodies obtained in this way, and seeds treated with this salt were 

 found to be immunized to some extent, although not entirely or invariably, 

 against this action." 



The influence of arsenic on the bacterial activities of a soil, J. E. Greaves 

 {Sci. Mo., 5 {1917), No. 3, pp. 204-209).— This is a review of work on the sub- 

 ject at the Utah Experiment Station, it being pointed out that arsenic by various 

 means stimulates the bacterial activities of soil, which results in greater crop 

 yields. " This increased growth must be looked upon as due to a stimulant 

 and not to the direct nutritive value of the substance added, and soils so 

 treated would wear out more quickly and produce larger crops than would 

 soils not so treated. It is . . . important to know that arsenic has to be 

 applied to a soil in enormous quantities before it retards microscopic plant life, 

 and most likely before it retards the growth of higher plants." " Other experi- 

 ments have demonstrated that the addition of arsenic to a soil causes the lib- 

 eration of the insoluble plant foods of the soil, especially the phosphorus. 



The effects of alkali salts on nitrification, P. E. Brown and E. B. Hitchcock 

 {Soil Sci., 4 {1917), No. 3. pp. 207-229, figs, i^).— Experiments conducted at the 

 Iowa Experiment Station to determine the concentration at which various 

 alkali salts become toxic to nitrifying bacteria in alkali soil and in normal 

 soil are reported. 



