568 Journal of Agricultural Research voi. xv, No. 10 



A summary of the results of the study of types of New York State 

 leaf roll shows the following conditions :• 



1. There is not always a definite correlation between external symp- 

 toms and internal changes. Typical leafroll plants may not always 

 exhibit pathological changes in the tissues. 



2. The type of necrosis is that described for European leafroll. 



3. In case of severe attack, American varieties showed a more striking 

 pathological condition than did the European varieties under observation. 



CONCLUSIONS 



The anatomical studies of both European and American leafroll have 

 failed so far to show a distinct correlation with the external symptoms 

 exhibited by the plant. It is true that in case of severe attack, recogni- 

 zable by external symptoms as such, we get the same pathological con- 

 dition; but there are exceptions which do not permit a wide generaliza- 

 tion. Typical leafroll plants which early show external symptoms often 

 fail to show extensive necrotic conditions, while plants affected with 

 trouble apparently other than leafroll, exhibit severe pathological 

 changes in phloem and cortex. The writer, however, is fully aware that 

 only one generation of plants has been studied and consequently he is 

 not in a position to give full assurance that he was dealing always with 

 hereditary leafroll. Should a study of the progeny of these plants estab- 

 lish the heredity nature of the disease as well as the constancy in the 

 symptoms, it might then be possible to separate or unite the various 

 types of leafroll on the basis of these symptoms. 



There is, however, some reason to suspect that the development of 

 necrotic tissues is not confined to plants affected with leafroll, but that 

 it is common to the so-called degeneration troubles in general, and per- 

 haps to others also. 



The pathological changes are most striking in the distal, growing 

 region of the stem. In sections taken farther down and especially at the 

 basal region, signs of pathological changes are less frequent and often 

 not found at all. An acropetal advance of internal symptoms, as claimed 

 by Quanjer (6) for "secondary diseased" plants, has not been observed in 

 this study. Similar observations have been made by Schander and 

 Tiesenhausen (7) who report the earliest and most frequent occurrence 

 of phloem necrosis in the upper part of the stem and especially in the 

 region just below the insertion of the leaves. 



The primary phloem groups are probably the first to suffer the effects 

 of the disease. The first symptoms, as far as this study is able to show, 

 consist of the separation of the primary walls of the phloem cells of an 

 individual group, resulting in the formation of intercellular spaces which 

 are filled with a secretion which is usually yellow in unstained sections. 

 In advanced stages the primary wall of the cells, bordering these cavities, 

 is also discolored. The size and extent of these spaces may increase to 



