44 PLANT DISEASES 



withdraws from the tent and closes the opening. Care 

 must be exercised in applying this method of treatment, 

 as the potassium cyanide and the gas generated are 

 poisonous.— Webber, U.S. Dept. Div. Veg. Phys. and 

 Path., Bull. No. 13. 



Sterilising Soil. — As already stated, it often happens 

 that where large numbers of plants are grown in a limited 

 space, and consequently crowded, a wave of disease 

 spreads rapidly, not unfrequently destroying the entire 



crop. 



When this occurs in houses, the most certain method 

 for preventing a reappearance of the disease, especially 

 if it is intended to continue growing the same kind of 

 crop, is to remove the whole of the soil, thoroughly 

 sterilise the building from top to bottom with a solution 

 of iron sulphate, and put in fresh soil. 



Where the disease is due to a root parasite, as in the 

 ' sleeping ' disease of tomatoes, this method is undoubtedly 

 the most reliable, and in the end least costly. 



However, practical men state that this method is not 

 always practicable; consequently the next best thing to 

 do is to sterilise the soil — that is, endeavour to destroy 

 all the mycelium, resting-spores, sclerotia, etc., that may 

 be present. 



This can be effected with more or less certainty — 

 depending on the thoroughness with which the work is 

 done — by various methods. 



Thoroughly mixing the soil with quicklime, where the 

 crop will admit ; or watering with a solution of soluble 

 phenyle, or with a liquid known in the trade as Jeyes' 

 fluid. The proportions for either of the two last men- 

 tioned substances are, one ounce to a gallon of rain-water. 



