BY THE CAREFUL use of hydrocyanic-acid gas in ac- 

 cordance with the directions given in this bulletin 

 practically all insects infesting the foliage of ornamental 

 plants in greenhouses may be controlled, and more 

 cheaply and elTectively than by any other means. 



In fumigating a house containing a large variety of 

 plants, using the correct dosage and under proper con- 

 ditions, the tender growth of some plants may be injured. 

 This injury is not permanent, however, and such plants 

 will show new vigorous growth in a short time. More- 

 over, the growth of many plants is stimulated by hydro- 

 cyanic-acid gas. 



Chemicals required in fumigating with hydrocyanic- 

 acid gas are sodium cyanid containing not less than 51 

 per cent cyanogen (or potassium cyanid containing not 

 less than 38.4 per cent cyanogen), sulphuric acid 93 per 

 cent pure, and water. Cyanid for fumigation purposes 

 should be practically free from chlorin. 



Fumigation should not be luidertaken in daylight or 

 when the temperature in the greenhouse is below 52° F. 

 or above 70° F. 



Cyanid is one of the most poisonous substances known. 

 Care should be taken to observe the precautions stated on 

 pages 11 and 12. 



