FOOT-ROT DISEASES OF WHEAT IN AMERICA if 
show visible signs of attack at this time, but there is no outstanding 
manifestation of the disease even in areas known to be infested by 
the causal organism. In general, these observations seem to be in 
accord with those made by Hori (3/7), who has studied this disease 
on barley, wheat, and rye in Japan. 
In the spring the disease may appear in large or small areas, and 
it frequently causes a spotting in fields, as shown in Plate I. Often 
many small spots are scattered throughout infested fields, giving 
' them a very ragged appearance, as shown in Plate I, B. These 
a? 
spots are very conspicuous on account of the bleached-yellow or red- 
dish yellow color of dead or dying plants. In some cases the diseased. 
plants may break over at the base, but from the writer’s experience 
this seems to be the exception rather than the rule. Frequently the 
disease may not appear until late in the development of the wheat 
plants, causing a bleaching of the whole plant, producing the condi- 
tion called white-heads in Australia. Plants showing white-heads 
may occur in spots or they may be scattered singly or in small groups 
throughout a large area. 
DISEASE SYMPTOMS 
On the basis of the work of Davis it seems evident that the 
wheat plant may become infested by the take-all fungus at any time 
during its life. Although the work of Davis indicated that seedlings 
are more susceptible to infection than older plants grown under the 
same conditions, it is of interest to note that seedling blight is not 
commonly found under natural field conditions. Under experi- 
mental conditions, however, seedling infection and killing take place 
regularly, probably on account of the fact that a greater quantity of 
the organism is present in the artificially inoculated soil than in 
most field soils. Typical seedling injury caused by Ophiobolus 
graminis is shown in Plate Il. The specimens photographed were 
from an inoculation experiment in which a pure culture of the fun- 
gus was added to the soil when the seed was sown. Older plants 
infected with the parasite under natural field conditions are shown 
in Plate III. It will be noted that the aboveground portions of the 
‘diseased plants show a bronze to yellow coloration. The under- 
ground portion of the tillers, the crown, and the roots show brown 
to black lesions or a general brown to black coloration and rotting. 
Close examination of the blackened areas will show the presence of a 
crust of interwoven mycelium (“mycelial plate;” Pl. IV, A). On 
the stems this crust occurs on and under the coleoptile and leaf 
sheaths and is attached to them or to the stem. Under certain con- 
ditions the small black perithecia (Pl. IV, B and () of the parasite 
will be found on the inner side of the leaf sheaths with their beaks 
projecting through the outer surface. They may appear also on 
the roots. It is not uncommon, however, to find an abundance of 
disease in some localities without any development of perithecia on 
the affected plants. This condition also frequently: occurs on dis- 
eased plants growing under pure-culture conditions where O. gram- 
enis is the only fungus present. 
When plants are attacked after the seedling stage, they react in 
essentially the same manner as seedlings. In many cases the lower 
Jeaf sheaths of such plants are held together tightly and all the 
