CHAPTER Xai 
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 tothe 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 theinse¢ts. In 
case of coleus, infested with mealy bug, in a very 
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