W. F. Bewley 



167 



Sterilisation by steam. 



Twelve boxes of naturally infected soil and twelve of inoculated soil 

 were made, six of each being steamed for two hours and the remaining 

 twelve being left untreated to serve as controls. After cooling the whole 

 twenty-four boxes were sown in the usual manner, 100 seeds per box, 

 and the seedlings removed as soon as they became diseased. The seedlings 

 in the steamed soil were perfectly healthy, while the unsteamed controls 

 showed an average of 47 per cent, of diseased plants in each box. Apart 

 from the control of the disease the steamed soil gave much the best type 

 of seedlings. They were more healthy and vigorous and showed better 

 root development than those in the untreated soils. The steaming also 

 killed all the weeds. 



Sterilisation by baking gave similar results. 



Sterilisation by formaldehyde. 



Formaldehyde has long been recommended as a soil, fungicide. The 

 soil in the boxes was saturated with different concentrations of formalde- 

 hyde; it was then covered for 48 hours to allow the vapours to act. After 

 this time had elapsed the covers were removed and the soil allowed to 

 dry, and seeds were then sown in the usual way. The results are shown 

 in Table VII. 



Table VII. 



Our results show that all strengths of formaldehyde solutions from 

 2 per cent, upwards are effective in soil sterilisation, but the weaker 

 solutions are not sufficiently strong to completely sterilise the soil. Our 

 untreated controls in the above experiments gave an average of 48 per 

 cent, diseased seedlings. Further experiments showed that complete 

 sterilisation of the diseased soil could be carried out by the following 

 method. A formaldehyde solution is made by adding one ounce of 

 commercial formalin (40 per cent, formaldehyde) to 2h pints of water 

 {i.e. 1 in 50). The soil is saturated with this solution, covered with glass 



