U. S. DEPARTMENT OF AGRICULTURE. 



BUREAU OF PLANT INDUSTRY- BULLETIN NO. 81. 



B. T. GALLOWAY, Chirf of Bureau. 



EVOLUTION OF CELLULAR STRUCTURES. 



BY 



O. F. COOK AND WALTER T. SWINGLE. 



VEGETABLK PATHOLOGICAL AND PHYSIOLOGICAL 

 INVESTIGATIONS. 



Issued August 4, 1905. 



WASHINGTON: 



GOVERNMENT PRINTING OFFICE. 

 1905. 



