48 R. GREIG-SMITH. 



Plants grown in a soil which has been heated, generally 

 show a remarkably fibrous root growth, 1 the aerial stems 

 are stouter, and the leaves are larger and deeply coloured. 

 They flower earlier and more abundantly. It is remarkable 

 that, while treating the soil with a volatile disinfectant 

 has much the same defect as dry heat upon the numerical 

 decrease and increase in the bacterial flora, the effect upon 

 plants grown in the soil is quite different. Those grown in 

 disinfected soils do not show the above changes in any 

 marked degree. 



The Action of Volatile Disinfectants. 

 The action of carbon disulphide upon the flora of the soil 

 was first investigated by Hiltner and Stormer 2 who in 1904 

 showed that the bacteria were considerably reduced in 

 number. This was followed by an increase so pronounced, 

 that at the end of a month after the evaporation of the 

 disinfectant, the original number of 9J millions per gram 

 of soil had risen to 50 millions. Then the number slowly 

 fell, but remained above the original number. In the 

 untreated original soil, the number remained for some time 

 fairly constant at 9J millions, and the ratio of the kinds or 

 groups was also constant. 



The flora of the normal soil consisted of 75% of non- 

 liquefiers, 20% of streptothrix species and 5% of gelatin- 

 liquefiers. As a result of the treatment with carbon 

 bisulphide, the non-liquefiers were greatly increased, and 

 the streptothrix varieties were strongly reduced, 3 and did 



1 Eussell and Petherbridge, Journ. Agr. Sci., 6, 248. 



2 Cent. Rakt. 2 te., 12, 126. 



3 This was not the experience of Eussell and Hutchinson (Journ. Agr. 

 Sci., 3, 111) with toluene. They found that the white and brown strep- 

 tothrix forms suffered less than the bacteria, and indeed that, after 

 toluening, the white streptothrix was the principal organism present in 

 the soil. The brown streptothrix suffered more than the white from the 

 treatment. Heat differs from toluene and readily destroys the white 

 streptothrix. 



