Apr. 31.1923 Occurrence and Significance of Phloem Necrosis 239 
organs. The first appearance of such a diseased area is exhibited by 
a swelling in the cell wall, often accompanied by discoloration. At a 
later stage, browning of the walls is noted, while at the same time the 
!Fig. I. —Stem section of young normal potato plant, showing general anatomical arrangement of vascular 
and fundamental tissues. 
lumen is partly or entirely filled with a gummy deposit which is homoge¬ 
neous or granular in nature. The parenchyma cells in the region where 
phloem fibers are differentiating show commonly an abnormal swelling, 
local in nature or extending laterally to include the walls of the peri- 
hperal phloem cells. 
