440 BOTANICAL GAZETTE [ DECEMBER 
the other. From yellow there is a gradual change to brownish 
red, the tissues in the meantime becoming considerably shrunken, 
Finally the pair of needles fall, this often being hastened by 
rain, wind, or any sudden jarring or shaking of the tree. In 
from three to six weeks after the fungus breaks through the 
tissues most of the leaves have fallen. Trees badly affected are 
the first to shed their leaves, defoliation being very rapid and often 
completed before the last-formed needles have attained full size. 
MICROSCOPIC STUDIES OF THE FUNGUS. 
Turning our attention to the fungus itself and the mannerin 
which it produces the changes described, a microscopic study of 
transverse and longitudinal sections through the pale yellow 
spots found early in April shows, growing between the cells 
composing the mesophyll region, a coarse,’ colorless, septate 
mycelium, containing numerous granules and vacuoles (jigs. 10 
and zz). The mycelium is confined wholly to the intercellular 
spaces of the mesophyll region. It never penetrates the walls of 
the mesophyll cells, but in many cases adheres very closely to 
the latter, producing changes in the cell contents which will be 
described as we proceed. Wherever it comes in contact with 
the cells composing the endodermis or the resin ducts it is 
effectually turned aside (fig. 78). A comparison of the dis- 
eased and healthy tissues at this time will show no essential 
difference so far as thickness and size of cells are concerned. 
In unstained sections the entire cortical and fibro-vascular 
regions, as well as the resin ducts, appear intact. The contents 
of the mesophyll cells of the diseased leaf, however, are seen to 
be disorganized. The chlorophyll bodies have disappeared and 
in their place many large oil globules are seen. In the healthy 
cells the chlorophyll bodies are numerous and distinct, while 
there are few or no oil globules, In the cells around some of 
the stomata of the diseased leaf the contents are not only dis 
organized, but are yellow and partially opaque. The v-shaped 
cell below the stoma is usually not involved, but those around, 
and especially below, show the change in a marked manner. 
