818 
Journal of Agricultural Research 
Vol. XXXI, No. 9 
bodies which were produced 2 to 3 cm. above the soil line on plants 
still standing as in the soil, while others were from plants frozen in 
the bottom of the flowerpots where they had been placed. 
From the foregoing evidence it is clear that Ophiobolus graminis 
- will survive the winter in the mycelial and ascospore stages. Although 
there were cases when the fungus was killed during the winter, it is 
evident that, under certain conditions at least, the fungus can live 
through rather severe winter conditions. 
AGE OF WHEAT PLANTS IN RELATION TO SUSCEPTIBILITY 
In order to obtain data on the relation of age of wheat plants to 
susceptibility to Ophiobolus graminis , it was necessary to sow all of 
the seed used in any one experiment at one time and to apply the 
parasite at intervals throughout the development of the plants, or to 
plant the seed at intervals and inoculate the plants at one time. Both 
methods were used with satisfactory results. In this study four 
experiments (numbered I to IV) were conducted. 
Experiment I was conducted out of doors in soil contained in No. 
00 ash pails of 5 gallons capacity. Experiments II, III, and IV were 
performed in the greenhouse in Wisconsin soil-temperature-control 
tanks, and the temperature of the soil was held as near 18° C. as 
possible throughout the growth of the plants. In all of the experi¬ 
ments the water content of the soil was 55 per cent of the total water¬ 
holding capacity, and this percentage was maintained as constant as 
possible throughout the experiments by frequent weighings. An 
excess amount of seed was always planted in the containers, and after 
the plants had reached about the third-leaf stage they were thinned 
to a uniform number. The inoculum used in these experiments con¬ 
sisted of the mycelium of the New York strain of the parasite growing 
on the barley and oat-kernel medium previously described. 
In the series sown at one time the first inoculation was made 
when the seed was planted. In the series sown at intervals the 
whole series was inoculated at the time the last planting was made. 
Growing plants were inoculated by carefully removing the upper 2 
inches of soil from the pots, great care being taken not to cause undue 
injury to the roots. The mycelium of the parasite growing on the 
barley and oat-kernel medium was then added to the soil, the whole 
mass was well mixed and returned to the pots and carefully worked 
around the roots. Great care was taken to use cultures showing 
the same amount of growth and to add the same amount of medium 
to all the pots inoculated. In the control pots, in each case, an 
equivalent amount of sterile barley and oat medium was added to 
the soil in the same manner. 
In Experiments I and II, California Club wheat was used, and 
the seed was sown at one time. The inoculations were made at 
intervals of 2 weeks after sowing, the first inoculation being made 
in one set at the time of sowing. As shown in Table VIII, all of the 
inoculated plants in these two experiments developed take-all and 
all eventually succumbed. All of the plants grown in the uninocu¬ 
lated soil remained healthy and matured normally. The amount of 
infection produced in one of these experiments is shown in Plate 5. 
The plants from seed which was inoculated at the time of planting 
began to turn yellow soon after emergence, and most of them died 
while in the seedling stage. 
