HISTOLOGICAL STUDIES ON POTATO LEAFROLL ^ 



By Ernst F. Artschwager 



Agent, Cotton, Truck, and ForageCrop Disease Investigations, Bureau of Plant Industry, 

 United States Department of Agriculture 



COOPERATIVE INVESTIGATIONS BETWEEN THE BUREAU OP PLANT INDUSTRY OF 

 THE UNITED STATES DEPARTMENT OF AGRICULTURE AND THE AGRICULTURAL 

 EXPERIMENT STATION AT CORNELL UNIVERSITY 



INTRODUCTION 



External symptoms are often insufficient and sometimes misleading 

 in the identification of certain plant diseases, and the pathologist must 

 resort to the studies of internal morphology and physiological reaction 

 to bring otherwise problematical questions to a satisfactory conclusion. 



The necessity of such an attitude is most clearly exemplified in the case 

 of the Irish potato leafroll diseases, which have been the subject of much 

 discussion and controversy for the last decade, both in this country and 

 in Europe. 



The literature of potato leafroll is voluminous and varied. The most 

 important articles, about 600, were reviewed by Appel and Schlumm- 

 berger (j)^ in 1911, and about three years later this list was extended 

 by Orton {4), in which he reviews the history of this disease and related 

 troubles and the theories regarding its cause. 



The ready identification of leafroll in the field and its separation from 

 other maladies is difficult, and there is much confusion over diagnosis. 

 Our knowledge of the pathological physiology of this disease is incom- 

 plete, and an understanding of the histological changes in the diseased 

 tissues is only in its beginnings. Very little is known in regard to the 

 chemical changes which acdompany the disorganization processes in the 

 cells and tissues, and nothing definite is known about the origin and 

 progress of the disorganization which sometimes leads to a complete 

 obliteration of the walls and contents of the elements of the conducting 

 system for plastic materials. 



The pioneer researches of Quanjer (5) have given an impetus to new 

 investigations along the lines just mentioned and have diverted our views 

 from the fungus culture to the histological and physiological side of the 

 problem. 



' This work was begun in the field laboratory of the Office of Cotton, Truck, and Forage Crop Disease 

 Investigations at Greeley, Colo., in the summer of 1916, and was continued in the Department of Plant 

 Pathology at Cornell University under the direction of Prof. H. H. Wlictzel and Dr. H. A. Edson, to whom 

 the writer wishes to express his gratitude for their courtesy and helpful suggestions. To Dr. A. J. Eames, 

 of the Department of Botany at Cornell University, the writer is especially indebted for the constant advice 

 and criticism received in preparation of materials, interpretation of slides, and editing of the paper. 



' Reference is made by number (italic) to " Literature cited," p. S70. 



Journal of Agricultural Research, Vol. XV, No. 10 



Washington, D. C. Dec. 9, 1918 



qn Key No. G-167 



(559) 



