560 Journal of Agricultural Research voi. xv, no. 10 



While taxonomic, inheritance, and control studies are being carried 

 on at present by various investigators, the following studies have for 

 their purpose the testing of Quanjer's hypothesis with both European 

 and American material, and the adding of new facts to the already exist- 

 ing knowledge. A former paper (2) on the anatomy and development 

 of the normal Irish potato plant furnished a background for the patho- 

 logical study and facilitates a more accurate interpretation of the existing 

 conditions. 



It is realized that an adequate inquiry into the problem of potato leaf- 

 roll from the viewpoint of the morphologist should first of all comprise 

 a detailed seasonal study of the normal plant grown under different 

 ecological conditions, with the purpose of correlating the influence of 

 external factors with changes in internal anatomy. These investigations 

 should then be extended to a study of plants affected with diseases of 

 parasitic and physiologic origin, to determine in how far the delicate 

 internal structures respond to the stimulating effect of parasites and their 

 toxins, as well as to unfavorable conditions of growth. 



A detailed microscopical study extending over several generations 

 should make it possible to trace the development of the disease from the 

 first cell response through the various chaiUges, culminating in the cessa- 

 tion of function and death; while microchemical investigations should 

 afiford an insight into the physiological activities of 'the diseased plants, 

 especially in respect to assimilation and translocation. A critical study 

 of the data obtained should either emphasize or discredit the value of 

 comparative anatomical studies for diagnostic purposes, and might permit 

 a grouping or separation of diseases on the basis of pathological anatomy 

 according as the symptoms found were similar or unlike. 



Present circumstances make it necessary for the writer to interrupt 

 studies of this character for an indefinite period while they are still in- 

 complete and preliminary, but sufficient progress has been made on a few 

 of the general questions of foremost interest to justify their presentation 

 in the hope that they may be of interest and value to other investigators. 

 This paper will be limited to the presentation of a comparative study of 

 certain European and American types of leaf roll, together with observa- 

 tions on the progressive histological changes in the tissues. 



EXPERIMENTAL MATERIALS AND METHODS 



Tubers for the study of European leafroll were obtained from Dr. 

 Quanjer, Wageningen, Holland, and from the Agricultural College, 

 Copenhagen, Denmark. The material representing American leafroll 

 was obtained from the Government station in Greeley, Colo., and from 

 various places in the State of New York. 



The methods of killing, fixing, embedding, and staining the material 

 were the same as those used (2) for the normal Irish potato {Solanum 

 tuherosum). 



