U. S. DEPARTMENT OF AGRICULTURE. 



BUREAU OF PLANT INDUSTRY— BULLETIN NO. 81. 



B. T. GALLOWAY Chief of Bureau. 



EVOLUTION OF CELLULAR STRUCTURES. 



BY 



O. F. COOK AND WALTER T. SWINGLE. 



VEGETABLE PATHOLOGICAL AND PHYSIOLOGICAL 



INVESTIGATIONS. 



Issued August 4, 1905. 



WASHINGTON: 



GOVERNMENT PRINTING OFFICE. 



1905. 



