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fumes need to be confined for one hour, after which it 

 should be thoroughly ventilated. If the fumes are con- 

 fined in a tight room, means for opening the ventilators 

 should be provided from the outside, and one should not 

 attempt to enter until after the place has been well venti- 

 lated. 



In fumigating the greenhouse the above quantities are 

 sufficient for 1,000 cubic feet of space where plants are 

 growing. Greenhouse plants vary greatly in their ability 

 to withstand the effects of hydrocyanic acid gas, and plants 

 such as tomatoes, roses and ferns are easily injured. In 

 the greenhouse the fumigation should be done at night 

 when there is no wind, and the house should be as dry 

 as possible, and at 60 degrees temperature. 



Pyrethrum 



This is a very fine, light brown powder made from the 

 flower heads of a certain species of Pyrethrum. It is prac- 

 tically harmless to man, but the fumes which it liberates 

 on exposure to air are suffocating to insects. It appears 

 on the market in three commercial forms: 



Persian insect powder, made from the heads of pyreth- 

 rum roseum, a plant native to the Caucasus region and 

 found under cultivation in America. Dalmatian insect 

 powder, and Buhach, made from Pyrethrum cinerariae- 

 folium. This is grown in California for this special pur- 

 pose. 



Any of these insect powders, when fresh and pure, are 

 effective for their purpose, but they quickly lose their ef- 

 fectiveness on exposure to air. These powders are usually 

 used by being sprinkled around over the insects, or in 

 places frequented by insects, -such as house flies and mos- 

 quitoes. They may be mixed with water and sprinkled 

 over the plants. 



Tanglefoot 



This is the material from which sticky fly paper is 

 made, and is useful for painting a ring around the base of 



