Nov. 1 , 1925 
OpJiiobolus graminis and Take-All of Wheat 
823 
and at the second-leaf stage (15 days old) the first leaf began to 
turn yellow. Some plants showed this chlorotic condition before 
the first leaf appeared, but these were only occasional cases. The 
bright-green color of the leaf faded out, leaving a yellow color in its 
place. At times this area turned bronze instead of yellow. The 
discoloration usually started first at the tip of the leaf and extended 
down the blade, but it often started back of the tip or on one edge. 
Finally, the whole leaf yellowed and died and turned a light-brown 
color. In a very short time the second leaf also became discolored 
similarly to the first one and died. Some of the infected plants 
recovered and lived indefinitely. Usually the primary root system 
on these plants was gone and part of the permanent roots was badly 
decayed, but new ones were formed to replace them. In case the 
plant had sufficient vitality to form new roots as fast as the fungus 
killed the old ones it lived, but if its vitality was low and new roots 
were not formed it soon died. In this event the roots became 
entirely decayed and the culm turned a dull-black color for about a 
centimeter above the soil line. 
The embedded material for the histological studies was sectioned 
5 to 10 microns in thickness and stained in saffranin and light green. 
These stains proved satisfactory and enabled the writer to follow 
the fungus fairly readily. Often the mycelium grew along the sur¬ 
face of the tissues and formed a mat of hyphae before penetrating 
the cells. The mycelium penetrated the wall at any point. Occa¬ 
sionally there was a swelling of the hyphae on each side of the wall, 
with constrictions of the segments in the wall. 
The fungus was found to enter the plant at any point below the 
surface of the soil. The coleorhiza was the first tissue found invaded, 
and the parasite often spread from this point into the developing 
root. However, the primary infection of the seedling took place 
chiefly by the fungus growing between the coleorhiza and the root, 
with subsequent penetration. As the root elongated, it became 
invaded at points below the primary infection, and in case the basal 
parts escaped infection, as they often did, the root was usually 
attacked at other points. After the fungus had entered the root it 
spread in all directions. However, usually the fungus did not 
spread lengthwise as much as it did toward the center of the root, 
as shown in Plate 6, B, because the root was being penetrated at 
various points along its entire length. On reaching the endodermis 
of the young root, the fungus stopped its inward growth and did not 
S enetrate this until most of the cells of the cortex had been killed. 
iven after penetrating the central cylinder the fungus appeared to 
remain, for the most part, in the parenchymatous cells, and was 
found inside the bundles of only the old and very badly diseased 
plants. 
The fungus invaded the leaf sheaths and culms in the same manner 
as the roots, penetrating at all points below the surface of the soil. 
The fungus was found in all the tissues of this region except the 
primordia. Frequently the coarse type of mycelium was found in 
the vessels of the lower portion of plants inoculated in large test 
tubes. 
Badly infected plants are usually black at the base. This black¬ 
ening may occur under the outer leaf sheath or it may show through 
