October 17, 1913] 



SCIENCE 



535 



yet been made of the presence in normal 

 soils of any factor which inhibited crop- 

 production. The last twenty years have 

 seen a wonderful advance in soil science. 

 Our knowledge of nitrification and ammo- 

 niacal fermentation has been much ex- 

 tended. The part played by the nodule 

 organisms of the leguminosfe has been well 

 worked out, has seen a newspaper boom, 

 and a subsequent collapse, from which it 

 has not yet recovered. But the greatest 

 advance has been the discovery of the part 

 played by protozoa in the inhibition of 

 fertility. 



The suggestion that ordinary soils con- 

 tained a factor which limited their fertility 

 emanated in the first instance from the 

 American Bureau of Soils. The factor was 

 at first thought to be chemical, and its pres- 

 ence was tentatively attributed to root ex- 

 cretion. Certain organic substances, pre- 

 sumably having this origin, have been iso- 

 lated from sterile soils, and found to retard 

 plant growth in water culture. It is 

 claimed, too, that the retardation they cause 

 is prevented by the presence of many ordi- 

 nary manurial salts with which they are 

 supposed to form some kind of combination. 



Contributions to the subject have come 

 from several quarters, but whilst the sug- 

 gested presence of an inhibitory factor has 

 been generally confirmed, its origin as a 

 root-excretion and its prevention by manu- 

 rial salts has not received general confirma- 

 tion outside American official circles. The 

 matter has been strikingly cleared up by 

 the work of Russell and Hutchinson at 

 Rothamsted, who observed that the fertility 

 of certain soils which had become sterile 

 was at once restored by partial sterilization, 

 either by heating to a temperature below 

 100° C, or by the use of volatile antiseptics 

 such as toluene. This observation suggested 

 that the factor causing sterility in these 

 cases was biological in nature, that it con- 



sisted, in fact, of some kind of organism 

 inimical to the useful fermentation bacteria, 

 and more easily killed than they by heat or 

 antiseptics. After a long series of admira- 

 ble scientific investigations these workers 

 and their colleagues have shown that soils 

 contain many species of protozoa, which 

 prey upon the soil bacteria, whose numbers 

 they keep within definite limits. Under cer- 

 tain circumstances, such, for instance, as 

 those existing in the soil of sewage farms, 

 and in the artificial soils used for the culti- 

 vation of cucumbers, tomatoes, etc., under 

 glass, the protozoa increase so that the bac- 

 teria are reduced below the numbers requi- 

 site to decompose the organic matter in 

 the soil into substances suitable for absorp- 

 tion by the roots of the crop. Practical 

 trials of heating such soils, or subjecting 

 them to the action of toluene, or other vola- 

 tile antiseptics, have shown that their lost 

 efficiency can thus be easily restored, and 

 the method is now rapidly spreading among 

 the market gardeners of the Lea Valley. 



I have attempted to sketch the chief 

 points of this subject with some detail in 

 order to show that strictly scientific work, 

 quite outside the scope of what some people 

 still regard as "practical," may result in 

 discoveries which, apart from their great 

 academic interest, may at once be turned to 

 account by the cultivator. The constant 

 renewal of expensively prepared soil which 

 becomes "sick" in the course of a year or 

 so is a serious item in the cost of growing 

 cucumbers and tomatoes. It can now be 

 restored to fertility by partial sterilization 

 at a fraction of the cost of renewal, and 

 considerable sums are thus saved by the 

 Lea Valley growers. 



For my second instance of scientific work 

 which has given results of direct value to 

 farmers, I must ask to be allowed to give 

 a short outline of the wheat-breeding inves- 

 tigations of my colleague Professor Biffen, 



