136 FUMIGATION METHODS 



Gowan will stand one-tenth of a gramme of 98 per 

 cent, cyanide per cubic foot of space for fifteen minutes 

 without material injury. This will kill about 90 per 

 cent, of the plant-lice, but will not kill thrips. The 

 use of the gas for carnations needs to be more carefully 

 investigated before it is recommended. The same is 

 true of chrysanthemums, on which it has been tried 

 with only partial success, the young growth being 

 very sensitive. 



Grapes under glass. The gas has been used with 

 success in New Zealand for the mealy bug, DaElylopius 

 adonidum L,, at the rate of one-third of an ounce 98 

 per cent, cyanide to 100 cubic feet. This is equivalent 

 to nine-hundred ths gramme per cubic foot. The gas 

 is liberated after dark and left in till next morning, 

 when thorough ventilation is given. It largely 

 escapes, however, during the night. The treatment 

 is said not to injure the plants in the least. 



Tomatoes. Dr. J. Fisher, on October 29, 1898, 

 reports using the gas for white fly {Aleyrodes sp. ) on 

 tomatoes. The gas from one ounce of pure cyanide of 

 potassium for each 1,000 cubic feet, left in the house 

 over night, killed all the insects without injury to the 

 plants. This method should receive careful trial by 

 other experimenters. 



Other experiments in greenhouses. For some years 

 in the large greenhouses connected with the Massa- 

 chusetts Agricultural College considerable difficulty 

 has been experienced with mealy bugs and various 

 species of scale insects on large vines, palms, begonias, 

 orange trees, acacias, etc. After a thorough trial of 



