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LETTER OF TRANSMITTAL 
United States Department of Agriculture, 
Bureau of Entomology, 
Washington, D. C, September 11, 1912. 
Sir: I have the honor to transrAit herewith, for publication as 
Bulletin No. 90 of this bureau, three papers comprising a report on 
an investigation of hydrocyanic-acid gas fumigation of citrus orchards 
in southern California. The preliminary report on the subject was 
published as Bulletin No. 79 of this bureau under the title " Fumi- 
gation Investigations in California." The present final report is 
divided into three parts, which were published separately on May 10 
and 13, 1911: I, entitled "Fumigation of Citrus Trees," by R. S. 
Woglum, a special field agent of this bureau, containing the main 
report on the field investigations and discussing the various details 
of fumigation procedure; II, a paper by Mr. Woglum, "The Value of 
Sodium Cyanid for Fumigation Purposes"; and, III, one by Mr. C. C. 
McDonnell, Chief of the Insecticide and Fungicide Laboratory, 
Bureau of Chemistry, "Chemistry of Fumigation with Hydrocyanic- 
acid Gas." 
Respectfully, L. O. Howard, 
Entomologist and Chief of Bureau. 
Hon. James Wilson, 
Secretary of Agriculture. 
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