868 
Journal of Agricultural Research voi. xxm, no. « 
blight occurred. The critical soil temperature for the development of 
of seedling-blight of corn, therefore, is about 20° (fig. 7). Here, again, 
the mean daily soil temperature in the field corresponded very closely 
with the constant soil temperature in the tanks in the greenhouse. 
These facts seem rather significant to the understanding of the relation 
of environment to the susceptibility of the hosts to this disease. They 
indicate, at least, that in this type of disease soil temperature is important 
as an environmental factor, and, further, that mean soil temperatures 
over periods of considerable duration are more influential as factors 
than brief extremes in soil temperature. 
SUMMARY 
(1) The seedling-blight of wheat caused by Gibberella saubinetii is 
manifest first by blighting before emergence, which results in poor germi¬ 
nation, second by blighting after emergence, which is evident by the 
yellowed and wilted seedlings, and third by stunting the seedling which 
is due to the weakened root system. 
(2) The symptoms of the seedling-blight of corn, caused by this same 
organism, are, in general, similar to those of wheat. 
(3) The invaded tissues in both wheat and corn become reddish brown 
to carmine red, depending upon environmental factors. 
(4) The disease develops from infected seed, scabbed seed m the case 
of wheat, and infested soils. 
(5) The period of seedling infection in both wheat and corn is usually 
limited to the early seedling stage. 
(6) With environmental factors favorable, the extent of blighting and 
injury from seedling-blight is directly proportional to the amount of 
infestation. 
(7) The parasite in pure culture functions normally over a compara¬ 
tively wide range of temperature, namely, from 3 0 to 32 0 C. The opti¬ 
mum temperature for spore germination, vegetative development, and 
sporulation is about 24 0 on unacidified and 28° on acidified media. 
(8) Wheat is a low-temperature plant and functions best at a low soil 
temperature in all stages of its development. On the other hand, com is 
a comparatively high-temperature plant and develops best at high soil 
temperatures. 
(9) The temperature of the soil is undoubtedly the most important 
single factor determining the extent of seedling-blight. The most 
favorable soil temperature for the blighting of wheat ranges from 12 0 to 
28° C. Below 12 0 no blight occurred if other factors were favorable. In 
contrast, the most favorable soil temperature for the blighting of com 
ranges from 8° to 20°. Above 24 0 no blight occurred. 
(10) Low soil moistures favor blighting of wheat even at low soil 
temperatures. 
(11) Results from sowings of wheat and com made at different dates 
under field conditions agree with those from the greenhouse experiments. 
Seeding when the soil is cool, that is, spring wheat at the earliest safe 
date in the spring and winter wheat at the latest safe date in the fall, 
reduces seedling blight. On the contrary, seeding com when the soil is 
warm, that is, at the latest safe date in the spring, reduces seedling-blight. 
(12) There are sharp critical temperatures for the production of the 
blight of both wheat and com. The mean daily soil temperature in the 
field corresponds to the constant soil temperature in the soil-temperature 
tanks. The critical soil temperature for the seedling-blight of wheat is 
