METHODS OF PREVENTION AND REMEDIES. 53 



the work of the fumigatorium at that place. From his 

 letters and reports I have extracted the following di- 

 rections and suggestions : ' For each 300 cubic feet 

 of space enclosed (and in proportion for greater and 

 smaller spaces) one ounce of 98 per cent, potassium 

 cyanide, one ounce of sulphuric acid, and two ounces of 

 water will be required to generate gas of sufficient 

 strength to kill the insects. Double this strength, or 

 the same amount of materials to 150 cubic feet en- 

 closed, may be used upon woody plants without danger 

 of seriously injuring them. The greater strength 

 should be employed whenever practicable, as it will 

 ensure the death of the eggs as well as the active 

 insects.' 



" Imported plants are usually in a more or less dor- 

 mant condition, which lessens danger of injury. Mr. 

 Lounsbury writes, in his report of June, 1897, ' Injury 

 to the tips of new growth generally results. This in- 

 jury is in 110 wise serious, and is quickly outgrown. 

 The operators consider it a favourable indication, as 

 when such injury results it is quite certain that the gas 

 has been present in sufficient strength to destroy all of 

 the insects.' 



" With respect to fruit, I again quote from Mr. 

 Lounsbury's letter : ' I had had lemons and oranges 

 analysed after treatment, and found that after a few 

 hours not more than a trace of the gas remained in the 

 rind. There is much more natural cyanogen in a 

 single seed (so the analyst told me) than what remains 

 in the fruit from fumigation. We have no complaints 

 of any effect on the keeping qualities of the fruit.' 



" To generate the gas the required quantities of 

 cyanide and water are first placed in the generating 

 vessel, the cyanide being broken into small pieces 

 about the size of lump sugar. The operator then adds 

 the acid, pouring it slowly into the vessel to avoid 

 splashing, and immediately withdraws. 



" The above treatment is suitable for fruit and hardy 

 plants. Tender garden plants are usually imported in 



