LETTER OF TRANSMITTAL. 



U. S. Department of Agricut>ture, 



Bureau of Plant Industry, 



Office of the Chief, 



Washmgtov, I). C, 3Iay SI, 1905. 



Sir: I have the honor to transmit herewith, and to recommend for 

 pubHcation as Bulletin No. 81 of the series of this Bureau, the accom- 

 panying technical paper entitled '"•Evolution of Cellular Structures." 

 This paper was prepared by Messrs. O. F. Cook and Walter T. 

 Swingle, and has been sul)mitted by the Pathologist and Physiologist 

 with a view to its publication. 



The accompanying plate is necessary to a complete understanding 

 of the text of this bulletin. 



Respectfully, B. T. Galloway, 



Chief of Bureau. 

 Hon. James Wilson, 



8e(yretary of Agriculture. 



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