822 
Journal of Agricultural Research 
Vol. XXXI, No. 9 
graminis. The writer feels fairly confident that the leaves and heads 
of wheat plants growing in the open field are seldom if ever attacked. 
The dying of the upper parts of the plant evidently is due either to the 
inability of the roots and culms to allow sufficient food materials and 
water to reach these parts or to the development of toxic substances in 
the regions of infection. The first view is the one which has been 
generally held for this type of phenomenon, but data are now available 
which indicate that toxic substances are given off by some fungi, and 
these toxins are capable of causing plants to wilt (4) • Possibly both of 
these factors operate, but the former would appear to be the chief 
factor in this case, due to the great reduction of the root area and the 
partial clogging of the vessels. 
HISTOLOGY OF DISEASED WHEAT PLANTS 
Suitable material for the histological studies was obtained by killing 
and fixing diseased and healthy plants each day as the disease pro¬ 
gressed. Virgin soil was thoroughly sterilized by steam pressure, then 
Ophiobolus mycelium, previously grown on cooked cereals, was 
thoroughly mixed with the soil. This was placed in small cans, and 
disinfected Goldcoin wheat seed was planted at a depth of 1K inches. 
An equal number of uninoculated cans for growing control plants were 
also prepared in the same manner, except that no fungus was added to 
the soil. The cans were placed in constant-temperature tanks and 
the temperature of the soil was maintained at 12° C. The plants from 
an inoculated and an uninoculated can were carefully washed with 
water and the plants killed, embedded in paraffin, and later sectioned 
according to the usual technique. Various killing and fixing agents, 
as Flemming’s medium, Gilson’s, Camoy’s, and chrom-acetic solu¬ 
tions, were used. The material killed and fixed in Gilson’s fluid gave 
the best results for general histology, but such material was very poor 
for showing the detailed structure of the host ceils. Two series of 
such plants grown at separate times were prepared in the above 
manner. 
While pursuing these studies the macroscopic symptoms also 
were carefully noted. The first primary root broke through the 
coleorhiza two days after planting and three days later this root 
appeared slightly dark and watersoaked near its base. The next 
day this water-soaked area had turned a dark brown to black, and 
on the eighth or ninth day after planting the primary roots had 
become so badly decayed that they easily broke off. In the mean¬ 
time, as the other roots developed they were also attacked, and 
lesions developed which were similar to those occurring on the first 
primary root. Often a root showed several distinct and separate 
lesions, indicating that the fungus had penetrated at various points. 
The coleoptile emerged from the soil on the eleventh day and an 
examination of the lower part of this, next to the old seed, revealed 
a slight discoloration. The following day this portion of the seedling 
was dark brown, and the lesion was extending farther up. 
On the fourteenth day after planting the seedlings began to show 
symptoms just above the ground line. Brown streaks were visible 
on the coleoptile near the soil, but they did not extend up the sheath. 
The infected plants were decidedly smaller than the control plants 
