VI PEEFACE. 



All information, as acquired, of direct bearing on the fumigation 

 practice has been given freely to the public as soon as its economic 

 value was established, largely by means of addresses, demonstrations, 

 and printed reports. 



In the present bulletin an attempt has been made to present a 

 succinct account of the completed results of this fumigation investi- 

 gation as well as a brief treatment of the salient features of fumi- 

 gation as practiced in California at the present time. It is of the 

 nature of a handbook on the most up-to-date equipment, methods, 

 and directions in orchard fumigation. Full advantage has been 

 taken of the results of other investigators in fumigation: yet in such 

 cases due credit is given to the proper source. The information 

 given in Bulletin 79 of this bureau, which is a preliminary report on 

 this investigation, has been largely included in the present bulletin 

 in summarized form. 



The writer desires to acknowledge his indebtedness to the many 

 people who have assisted him during this investigation and facilitated 

 the progress which has been made. To Mr. C. L. Marlatt, Assistant 

 Chief of the Bureau of Entomology, he is especially indebted for 

 valuable assistance and advice. Acknowledgment is also due to 

 Mr. Frederick Maskew, who most capably assisted him in the per- 

 formance of many of his experiments during the period from Decem- 

 ber, 1907, to August, 1909. Valuable assistance was rendered by 

 Mr. E. R. Sasscer during the months of August. September, and 

 October, 1909. Mr. W. W. Yothers was engaged in the work during 

 November, 1909. To the Hon. J. W. Jeffery, State commissioner of 

 horticulture of California, credit is due not only for his activity in 

 paving the way for this investigation, but also for the able support 

 given by him since field work was commenced. To Mr. William Wood, 

 of Whittier. Cal., the writer acknowledges his indebtedness for 

 assistance in introducing the improved system of fumigation in the 

 region adjacent to Whittier, as well as for practical advice with regard 

 to citrus insects and their control, a subject about which Mr. Wood 

 is especially well informed. This occasion is also taken to thank the 

 various horticultural officers of southern California, packing-house 

 managers, and the many citrus growers who have assisted and sup- 

 ported this investigation. 



The cooperation of the Bureau of Chemistry of the United States 

 Department of Agriculture has been an important adjunct of this 

 investigation, and to Mr. J. K. Haywood, Chief of the Miscellaneous 

 Division of that bureau, and his assistants the writer is indebted for 

 the carrying out of all the chemical analyses and laboratory tests of 

 materials and products necessary to the working out of the field 

 experiments. 



R. S. W. 



