12 SCIENCE BULLETIN, No. 9. 



Russell and Hutchinson conduce to more vigorous growth, but that at the 

 same time certain toxic substances are formed which arrest plant growth, 

 but as these toxins are unstable and readily oxidised the toxic conditions da 

 not prevail for any length of time. 



F. Fletcher* obtained very much higher yields with maize plants grown in 

 soil previously heated, which results he attributes to the destruction by heat 

 of an alkaloid dihydroxystearate. He also finds germination injuriously 

 affected by previous heating. This he attributes to increased osmotic activity 

 which results in a decrease of imbibition, brought about by increase cf soluble- 

 organic substances. 



R. Greig-Smith,")" to some extent opposes the conclusions of Russell and 

 Hutchinson. The beneficial action of disinfectants, such as chloroform,, 

 toluene, &c., is explained by him as being due to the removal, by these 

 reagents (all of which are wax-solvents), of a wax-like substance (agricere) 

 with which the soil particles are coated. With the removal of this water- 

 proofing the soil nutrients are more easily dissolved in the soil-water and 

 attacked by bacteria. 



According to this investigator, the principal nitrogen-fixing bacterium in 

 soils is Rhizobium leguminosarum, the number of which affords an indication 

 of the comparative fertility of the soil, and which, in the most fertile soils,, 

 may be present to the number of three or four millions per gramme of soil. 

 He finds, further, that all soils contain a substance which acts as a bacterio- 

 toxin, fertile soils containing a small, poor ones a large amount. This toxin 

 is destroyed by heat, sunlight, and storage, and is washed into the subsoil 

 by rain, so that after a shower of rain the surface soil is richer in bacteria 

 than the lower strata. This latter is an extremely interesting observation, 

 as indicating that the beneficial effects of rain or of irrigation are not confined 

 to the mere supply of water or even of fertilising salts to the soil. 



These bacterio-toxins are insoluble in wax-solvents, and are not volatile. 



He finds also that after the protozoa have been destroyed by heat at 65 

 to 70, the action of volatile disinfectants is to increase still further the 

 bacterial productiveness of the soil. 



Additional indication that these disinfectants act as wax-solvents in dis- 

 solving the agricere, is afforded by the fact that the upper layers of soils so 

 treated are less nutritive to bacteria than the lower, which is what might be 

 expected if the disinfectant on evaporation carried the agricere to the 

 surface. 



Dr. Greig-Smith is reading a paper before this section, in which he 

 recapitulates his work in this connection. 



If the theory that the action of heat and of solvents is to destroy the 

 waterproof coating is correct, one would expect that the soils so treated 

 would yield more of their mineral ingredients to soil-solvents. The evidence 



* Cairo Sclent. Journ., 1910, 4, reprint (Abstract in Chem. Soc. Journ. Abstracts 

 vol. 100, ii, 350). 



\Proc. Linn. Soc., N.S.W., vol. 35, p. 808 ; vol. 36, pp. 492, G09, 679. 



