Nov. 1, 1925 
Ophiobolus graminis and Take-All of Wheat 
821 
An experiment similar to the one just described was conducted on 
the culms. For this purpose the plants were grown in tubes con¬ 
taining Crone’s agar. When the plants were about 4 inches tall, 
cooled potato-dextrose agar was poured into the tubes to a depth of one- 
half inch. Ophiobolus was placed in some of these tubes, and others 
were left uninoculated for controls. The culms began to turn dark 
at the surface of the agar soon after the mycelium had spread over the 
medium and had come in contact with the culm tissues. The 
darkening progressed up and down the culm, and as the agar dried 
away from the surface of the walls of the tubes, the fungus grew 
down through this opening and attacked the roots. The fungus 
spread through the agar to a very slight extent. As in the case of 
the roots, it was found that the fungus penetrates the leaf sheaths 
and culms at any point below the surface of the soil. Often isolated 
lesions were noted on the sheaths, thus indicating that the fungus 
had entered at that point (pi. 6, A). 
The green leaves of 10 plants in the early heading stage growing in 
the field also were tested for susceptibility to infection. Rubber 
rings, with a diameter a little less than the width of the leaves, 
were placed on the surface. A water suspension of ascospores was 
placed in these and a cover glass placed over each ring. The rings 
were held in place on the leaves with fine spring clamps. No infec¬ 
tion took place by this method of inoculation. A few of the spores 
sent out snort germ tubes, but they never entered the leaf. This 
method seemed unsatisfactory and it was discontinued because the 
water evaporated too rapidly and left the germinating spores dry. 
Numerous wheat heads grown in the field were dipped in an .asco- 
spore suspension and then covered with glassine bags. The bags were 
tied closely about the culm to prevent evaporation, and were allowed 
to remain in place for four days, after which they were removed. No 
sign of disease developed, and the heads matured good seed. Ten 
plants growing in pails in the greenhouse were thoroughly covered 
with a spray of ascospores and placed in a moist chamber. Part of 
the plants used were young, while others had headed out. The air of 
the chamber was kept saturated with moisture, and the temperature 
was held as near 20° C. as possible. The light conditions in the cham¬ 
ber were poor. After four days the plants were taken out of the 
chamber and placed in the greenhouse. No visible signs of disease 
appeared on the plants. Microscopical examinations showed that 
a number of the spores had germinated, but in no case had they 
penetrated the wheat plants. The plants were examined the day 
after they were removed from the moist chamber and at short intervals 
for several weeks, but no sign of disease appeared. Finally, bits of 
mycelium were placed on leaves and heads of 10 more plants. A 
needle was run through the masses of mycelium and into the tissues of 
the plant. The plants were placed in a moist chamber for four days 
under the same conditions as before. They were allowed to stand 
one day after being removed before being examined for infection. 
By that time the mycelium had dried up and none could be found in 
the tissues, except a few pieces pushed in with the needle. Later no 
mycelium could be found, and disease symptoms never developed. 
From the results obtained in these experiments, indications are that 
the leaves and heads are not susceptible to attack by Ophiobolus 
