PRESIDENTIAL ADDRESS. 



61 



given through the stimulation of the soil bacteria. This 

 appears to be the first suggestion of a direct and indirect 

 plant stimulation by disinfectants. 



I do not think that a direct stimulation of a growing plant 

 by a volatile disinfectant has been proved, although the 

 stimulation of germinating seeds has been known for some 

 time. The action of ether in hastening germination was 

 described to me when in Copenhagen in 1897. Koch 1 

 records the stimulation of weed seeds by carbon disulphide, 

 and Hamburger 2 says that chloroform in the proportion of 

 one to one hundred thousand parts stimulates the germin- 

 ation of seeds, while with one to one thousand parts the 

 germination is impaired. 



The effect upon the seed is probably caused by an increased 

 permeability of the cell- walls of the tissue by the action of 

 the disinfectant, and the consequent easier migration of 

 the enzymes to the glucosides. 3 



With regard to the stimulation of the bacteria by disin- 

 fectants, both Hiine and Fred employed bouillon for grow- 

 ing the organisms, and in concluding that a bacterial 

 stimulation occurred in the soil, Fred must have taken it 

 for granted that some of the disinfectant remained in the 

 soil in order that it might exert its effect. If the disin- 

 fectant has entirely volatilised when its presence cannot be 

 detected by the senses, all stimulating action must cease. 

 A sustained stimulation necessitates the continued action 

 of a stimulant. Heinze detected traces of carbon disulphide 

 in the soil a month after treatment, and recently I have 

 shown that traces of chloroform remain in the soil for at 

 least six months. At the same time I showed that small 

 amounts of chloroform stimulate the multiplication of 

 bacteria in soil extract. Soil extracts may be nutritive or 



1 Cent. Bakt., 2te, 31, 175. ' * Nature, 96, (1915), 19. 

 5 The Armstrongs, Proc. Koy. Soc, B. 84, 226. 



