THE PARTIAL STERILIZATION OF SOILS. 



243 



In order to use chemical substances for the control of the soil 

 population it is therefore necessary to know exactly what organisms 

 are to be dealt with, and to carry out direct experiments with those 

 organisms to ascertain the effects of the antiseptics on them. 



It is well known that poisons have a marked selective effect on 

 organisms. A substance may prove fatal to one kind of organism 

 but not to another ; there has to be a relationship between the 

 particular cell substance and the particular poison before killing 

 occurs. Heat, on the other hand, kills everything. 



Our first remedial scheme was drawn up as the result of observa- 

 tions in the nurseries. It was as follows : — 







Agent tried. 





Disease. 

















Steam. 



Cresylic Acid. 



Formaldehyde. 



" Soil sickness " 



Effective 



Effective 



Effective 



Wireworm 



Effective 



Not effective 



Not effective 



Club 



Effective 



Fairly effective 



Not certainly effec- 







tive 



Sleepy disease 



Effective 



Not certainly effec- 



Not certainly effec- 







tive 



tive 



Fusarium 



Effective 



Not effective 



Frequently effective 



Damping off 



Effective 



Not effective 



Effective 



Root fungus 



Effective 



Not effective 



Effective 



Stripe 



Not effective 



Not effective 



Not effective 



This chart indicated the proper method of attacking the problems 

 and has been adhered to in all subsequent work. 



Analysis of the soil population is made and the effect of different 

 substances on the individual is studied. The work is difficult and 

 highly specialized. 



Fortunately Mr. W. B. Randall of Waltham Cross came forward 

 at a critical moment and generously provided funds for the appointment 

 of a competent biologist, and fortunately also we were able to interest 

 Mrs. D. J. Matthews (formerly Miss Isgrove) in the problem ; she 

 therefore undertook the work. 



The method of procedure is as follows. The analysis of the soil 

 population is made partly by the plant and partly by the scientific 

 investigator. The indications of the plant are sometimes definite ; 

 for example, Root-knot indicates the eelworm Heterodera radicicola, 

 sleepy disease indicates Verticillium, damping off indicates Pythium, 

 &c. Laboratory methods have been worked out at Rothamsted 

 for studying other members of the soil population. 



Having thus made a survey of the population to be dealt with, 

 the investigator finds some means of estimating the number in one 

 gram of soil of the particular organism on which he is working. Then 

 the soil is treated with a certain weight of the antiseptic ; another 

 lot is treated with -fa that weight ; others with jfo, and so on- 

 On chemical grounds it is better to take the^ molecular weight and not 



