Dec.9, i9i8 Histological Studies on Potato Leajroll 567 



yellow secretion, or a combination of these. Plate C, figure 5, shows 

 such a group. We notice that most of the cells of the phloem are more or 

 less collapsed and filled with a granular precipitate ; between other cells 

 in the group intercellular cavities have been formed, the cells themselves 

 having remained normal. 



The basal region of the stem is normal, with an occasional disturbance 

 in the inner phloem. 



LEAFROLL IN TH© DOOLEY VARIETY, MATERIAI, A 



The material was obtained from a field near Seneca Castle, Ontario 

 County. The plant selected for study was dwarfed, spindly, erect, and 

 broomlike. The leaves were slightly reduced in size and folded along 

 the midrib. Discoloration of the foliage is only noticeable along the 

 margin of the leaflets. 



Sections through midrib show normal structures; a few of the groups 

 of the inner phloem have cells with walls and content disorganized. The 

 petiole is severely diseased (PI. 43, A) in that almost all of the external 

 and most of the internal phloem is necrotic. The vascular tissue of the 

 petiolar wings is abnormally developed; the large amount of phloem in 

 these groups is probably formed as a consequence of the destruction of 

 tlie phloem of the lateral and median bundles. Sections through the 

 basal region of the petiole show a decrease in the severity of the symp- 

 toms; there are a few diseased areas, especially in the outer region ex- 

 tending from the fibers in the peripheral and radial direction (Pi. 40, A, B). 



Upper stem sections show the symptoms described for the basal part of 

 the petiole, perhaps less extreme. There are a few phloem groups com- 

 pletely destroyed; and in such a region the cells of the pericycle are 

 always radially stretched. A few cells of the cortex are also diseased 

 and filled with the typical granular deposit. 



IvEAFROLE IN THE DOOLEY VARIETY, MATERIAL B 



Material B was obtained in the same field. The plants showed symp- 

 toms of severe leaf roll; reduction in size, broomlike appearance, rolling, 

 and pronounced reddish discoloration of the foliage. 



Microscopic sections through the upper nodal region (midrib and petiole 

 were not examined) show normal structures except for one large dis- 

 eased area which extends from the cortex to the xylem, involving some 

 of the elements of the latter tissue. Other stem sections through both 

 nodal and internodal region show normal structures. 



LEAFROLIv IN THE NEW YORK RURAE VARIETY 



This material was obtained from another field in Ontario County. 

 The plants exhibited the symptoms described for the above variety, 

 but microscopic examinations failed to show extensive abnormalities. 

 A few stem sections showed diseased cells in the cortex which were filled 

 with the granular precipitate. 



