CHAPTER XIV 

 GREENHOUSE AND COLD FRAME FUMIGATION 



T""|HE greenhouse problem in reference to insects 

 has been one of considerable importance. 

 Early in 1894 Dr - Albert F. Woods, assisted 

 by Mr. Dorsett, as noted in Chapter III., 

 began a series of experiments under glass with this 

 gas. They found that plants were less injured by a 

 short exposure to a relatively large amount of gas 

 than they were by a long exposure of a relatively 

 small amount. It was also shown that the stronger 

 dose a short time was most destructive to the insects 

 affecting the plants. In these experiments they 

 showed that different species and varieties of plants 

 varied remarkably in their power to withstand the gas, 

 depending upon the open or closed condition of the 

 breathing pores of the leaf, the cell contents, and tem- 

 perature of the inclosure. The plants fumigated were 

 ferns, coleus, double English violets, single violets, 

 roses, carnations,, grapes, tomatoes, and cucumbers. 



The amount of cyanide used per cubic foot of space 

 inclosed varied from 0.075 gramme to 0.15 gramme. 

 For instance, ferns, infested with a scale insect, sim- 

 ilar to the scurfy scale on apple, were fumigated at 

 night with 0.075 gramme 98 per cent, cyanide for 

 twenty minutes without injuring the most delicate 

 fronds, at the same time destroying all the insects. In 

 case of coleus, infested with mealy bug, in a very 



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