APPi:]SrDIX A 131 



A substance toxic to plants — dihydroxystearie acid — was also 

 formed by the heating process. If already present in the soil, the 

 quantity of dihydioxystearic acid was increased ; it appeared, how- 

 ever, even when lacking in the unheated soil. 



Sehreiner and Lathrop point out that, although the majority of 

 compounds formed when soils were heated must be classed as bene- 

 ficial, the harmful compound form.ed at the same time more than 

 counteracts their effects. If this harmful compoimd can be elimi- 

 nated or diminished, the full beneficial effects of heating will become 

 apparent. Such changes in the constitution of harmful substances 

 take place if a heated soil is allowed to stand in contact with the 

 air, and are probably due to oxidation. 



Soils may also be sterilized by the use of volatile antiseptics like 

 chloroform and carbon bisulphide. One or two per cent of the liquid 

 antiseptic is usually added to the soil and mixed. After allowing one 

 day for the antiseptic to act, the soil is spread out to allow it to pass 

 off into the air. This method gives only partial sterilization, yet its 

 use is usually followed by a large increment in ammonia and bacterial 

 activity, followed by improvement in plant growth. 



There are several theories concerning this beneficial action of 

 volatile antiseptics. Hiltner and Stormer'' propose a "Selective" 

 action, through which the equilibrium of microorganic life in the soil 

 is disturbed in such a way that ammonifying and other beneficial 

 bacteria become predominant. 



Kussell and Hutchinson^ hold a somewhat similar view. They 

 believe that the effect of partial sterilization is to kill off the larger 

 phagocytic organisms which devour the beneficial bacteria. 



Koch" and his associates believe that the small quantities of anti- 

 septics remaining in the soil exert a stimulating action upon bacteria 

 and green plants alike. 



Grieg-Smith* holds that soils, especially poor soils, contain a 

 bacteriotoxine which retards growth, and that the result of partial 

 sterilization with carbon bisulphide or by heat is a destruction of 

 these bacteriotoxines. 



The subject of partial sterilization by volatile antiseptics is in need 

 of thorough investigation from the standpoint of the organic chemist. 



Methods of sterilizing seed. In order to secure vigorous seedlings, free 

 from all microorganisms, great care must be exercised in sterilizing 



1 Jahresber. angew. Bot. 5 : 214. 1907. « Centralbl. f . Bakt., 2te Abt. , 31 : 185. 1911. 



2 Jour. Agr. Sci. 3 : 111. 1909. * Centralbl. f . Bakt. , 2te Abt. , 30 : 154. 1910. 



