652 PROCEEDINGS OF SECTION K. 



of the sick-soil of a commercial glass-house in which cucumbers 

 were grown resulted in curing the soil of cucumber-sickness, and 

 rendering it once more commercially profitable. The same was 

 found to be the case with tomato-sick soil on which a number of 

 different antiseptics were tried. Of all methods, heating the soil to 

 98° was found to be the most efficient. The cost of this operation 

 is from Is. to Is. 6d. per ton of soil, which, while profitable in the 

 case of plants grown under glass, is quite prohibitive on large 

 areas. 



S. U. Pickering [Journal of Agricultural Science, Vol. 3, 

 p. 277) considers that, on heating a soil, the soluble plant-food is 

 increased, and the changed bacterial conditions studied by 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 oxidized, the 

 toxic conditions do not prevail for any length of time. 



F. Fletcher {Cairo Scieiitific Journal, 1910, 4, reprint), (Ab- 

 stract in (Jhcm. Sac. Jouiii., ahstracts, Vol. 100, ii., 530) obtained 

 very much higher yields with maize plants grown in soil previously 

 heated, which results he attributes to the destruction by heat of an 

 alkaloidal dihydroxystearate. He also finds germination injuriously 

 affected by previous heating. This he attributes to increased os- 

 motic activity, which results in a decrease of imbibition, brought 

 about by increase of soluble organic substances. 



R. Greig-Sraith (Proc. Linn. Soc, N.S.W., Vol. 35, p. 808; 

 Vol. 36, p. 492; Vol. 36, p. 609; Vol. 36, p. 679) 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 Rhizohiiiui 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 ex- 

 tremely 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 fertilizing salts to the soil. 



