Part 3

_Secretary of Agriculture_ Henry C. Wallace. _Assistant Secretary_ Howard M. Gore. _Director of Scientific_ Work E. D. Ball. _Director of Regulatory Work_ Walter G. Campbell. _Director of Extension Work_ C. W. Warburton. _Solicitor_ R. W. Williams. _Weather Bureau_ Charles F. Marvin, _Chief_. _Bureau of Agricultural Economics_ Henry C. Taylor, _Chief_. _Bureau of Animal Industry_ John R. Mohler, _Chief_. _Bureau of Plant Industry_ William A. Taylor, _Chief_. _Forest Service_ W. B. Greeley. _Chief_. _Bureau of Chemistry_ C. A. Browne, _Chief_. _Bureau of Soils_ Milton Whitney. _Chief_. _Bureau of Entomology_ L. O. Howard, _Chief_. _Bureau of Biological Surrey_ E. W. Nelson, _Chief_. _Bureau of Public Roads_ Thomas H. MacDonald, _Chief_. _Bureau of Home Economics_ Louise Stanley. _Chief_, _Bureau of Dairying_ C. W. Larson, _Chief_. _Office of Experiment Stations_ E. W. Allen. _Chief_. _Fixed Nitrogen Research Laboratory_ F. G. Cottrell, _Director_. _Publications_ L. J. Haynes, _In Charge_. _Library_ Claribel R. Barnett. _Librarian_. _Federal Horticultural Board_ C. L. Marlatt, _Chairman_. _Insecticide and Fungicide Board_ J. K. Haywood. _Chairman_. _Packers and Stockyards Administration_ } Chester Morrill, _Grain Futures Administration_ } _Assistant to the Secretary_.

This bulletin is a contribution from

_Bureau of Chemistry_ C. A. Browne, _Chief_. _Microbiological Laboratory_ Charles Thou, _Mycologist in Charge_.

ADDITIONAL COPIES OF THIS PUBLICATION MAY BE PROCURED FROM THE SUPERINTENDENT OF DOCUMENTS GOVERNMENT PRINTING OFFICE WASHINGTON, D. C. AT

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Transcriber Note

Figure 1 was moved so that it would not split a paragraph.