840 
Journal of Agricultural Research 
Vol. XXIII, No. II 
The period of severe infection in both wheat and corn is usually re¬ 
stricted to the seedling stage. Few new infections occur after the seed¬ 
ling has reached the fourth-leaf stage. Occasionally, however, under 
weather conditions favorable for the development of the disease new 
root lesions may develop, which tend to reduce the vigor of the plant 
but rarely develop sufficiently to kill it. 
LIFE CYCLE OF THE ORGANISM IN RELATION TO THE PRODUCTION 
OF seedling-blight 
The seedling-blight of wheat and com develops from two chief sources; 
first, scabbed or infected seed and, second, infested soil. Floral infec¬ 
tions in wheat develop during moist, warm weather and result in blighted 
or scabbed kernels within the infected spikelets. 'The mycelium hiber¬ 
nates in or on the scabbed kernels, many of which show no marked external 
symptoms until the seed is sown, when the parasite develops in the 
young seedling. Seed infection also occurs in com. The mycelium 
hibernates in the seed and develops in the young seedling in the spring, 
following germination. 
In addition to seed infection, the organism develops as a saprophyte 
on decaying crop refuse near or on the surface of the soil. It becomes 
aggressive as a parasite only when the seedlings are weakened by un¬ 
favorable environment. 
EXPERIMENTAL METHODS 
culture methods 
The temperature and moisture studies were conducted under con¬ 
trolled conditions in the greenhouse as well as under field conditions. 
Pure-line Marquis wheat (Wis. Ped. No. 50) was used in all of the spring- 
wheat studies and pure-line Turkey wheat (Wis. Ped. No. 2) was em¬ 
ployed in the winter-wheat studies. Specially selected ears of Funk 
Ninety-Day yellow dent and Golden Glow yellow dent were used in all 
of the experiments. Only kernels free from disease and treated with 
mercuric chlorid 1 to 1,000, followed by rinsing, were used for inoculation 
and controls. In addition, naturally infected, scabbed wheat kernels 
were used in several experiments in comparison with artificially inocu¬ 
lated seed. 
In the greenhouse the soil-temperature experiments were conducted 
in the Wisconsin soil-temperature tanks, considerably modified from 
those described by Jones ( 21 ) and Johnson and Hartman (20). The 
tanks, as constructed on the unit plan, consisted of the insulated water 
bath equipped with a rigid cover through which the soil containers were 
suspended in the water bath below. 
Containers of two different sizes were used. A can 6 inches in diameter 
by 12 inches deep was used for most of the seedling studies, and a larger 
can 12 inches in diameter by 20 inches deep for the plant studies. In 
addition to being utilized as soil containers these larger cans were fitted 
with covers and used for culture chambers. These, together with the 
Altmann incubator, were used in the studies on the relation of tempera¬ 
ture to the development of the fungus. 
The water within the tank was heated by an electric heater in a water¬ 
tight copper container submerged at the bottom of the tank. The heater 
was controlled by a mercury thermostat set in the water bath and an 
