5° 



of recommendation. From the fact that no two greenhouses are ex- 

 actly alike in regard to tightness, it is impossible to give specific 

 directions to cover all cases, but it is safe to recommend the use of 

 an amount of potassium cyanide varying according to the tightness 

 of the house from .007 to .01 gm. per cu. ft. of space, for three hours' 

 time after sunset. No injury to tomato or cucumber plants would 

 result from using the larger amount, but it is believed that the smal- 

 ler amount in a tight house will prove as effective as the larger 

 amount in a loose house. Even .02 gm. per cu. ft. of space, as shown 

 by Experiment 15, can be used without injury to cucumber and to- 

 mato plants in a reasonable state of vigor. For tender plants like 

 tomatoes it is advisable to keep well t>elow the danger limit of the 

 tenderest leaves and use the potassium cyanide at rates not greater 

 than .01 gm. per cu. ft. of space. 



It is not within the scope of the present paper to give the minute 

 details of fumigating with this most powerful of all known destroyers 

 of animal life. 



Johnson's recent work, entitled " Fumigation Methods," is in- 

 dispensable to anyone who has occasion to use hydrocyanic acid gas 

 as an insecticide. This book can be purchased for $1.50 of the pub- 

 lishers, Orange Judd Company, 52 and 54 Lafayette Place, New 

 York City. To those interested in greenhouse fumigation the fol- 

 lowing pages are especially recommended : 9-1 1, 118, 124-146. 



Attention is here called to the fact that ventilation of the house 

 is necessary after the expiration of the three hours of treatment, and 

 that this is practicable only under such circumstances that no injury to 

 the plants will result from lowering the temperature of the house. 

 The amount of artificial heat that can be supplied, and the outside 

 temperature must be taken into consideration. Ventilation need not 

 be very prolonged nor very thorough immediately following the ex- 

 posure ; a few side ventilators opened (from the outside) for a quar- 

 ter of an hour will be sufficient. A more thorough ventilation should 

 be given before one ventures to inhale air while in the house. 



In order to be most successful, fumigation should be in accord- 

 ance with a knowledge of the life history of the insect. A single 

 fumigation at the rates recommended will destroy all of the insects 

 except those in the egg and some of those in the late pupal stage. 

 .It is desirable to fumigate again two weeks later, thus killing the 



