Mar. 17,1923 Influence of Soil Temperature on Seedling-Blight 847 
The time required for the production of conidia varied from about 20 
days at 4 0 C. to 24 hours at 30° to 32 0 . Sporodocia-like tufts of conidia 
were produced at the higher temperatures almost as an outgrowth of the 
conidium. The higher temperatures stimulate the early production of 
conidia by Gibberella saubinetii , as described by Dickson and Johann (9). 
INFLUENCE OF SOIL TEMPERATURE ON THE DEVELOPMENT OF HOSTS 
While it is not the purpose of this paper to discuss in detail the influ¬ 
ence of temperature on the development of wheat and corn, this being 
reserved for another paper, yet it is desired to give a brief summary in 
order to be able to present more clearly the relation of the hosts to the 
development of the disease. The results obtained have demonstrated 
that temperature is one of the 
major environmental factors in 
the physiology of the cereal crops; 
and, therefore, a knowledge of 
these temperature responses is of 
fundamental importance in ex¬ 
plaining predisposition to disease. 
The experiments likewise have 
shown that other factors, such as 
soil moisture and light intensity, 
greatly influence predisposition 
to disease. Either of these fac¬ 
tors, for instance, under certain 
conditions, may completely over¬ 
shadow temperature. The study 
of environmental factors con¬ 
cerned in the development of the 
seedling-blight has served to bring 
out clearly the fact that all the 
environing conditions are insepa¬ 
rably connected and that the de¬ 
gree of blight is the product of a 
number of factors, any one of 
which when varied may start a 
similar set of reactions within 
the host or parasite. It seems 
necessary, therefore, to study the responses set up by these environing 
factors, not only in the parasite but in the healthy host as well. 
6 /2 16 20 24 28 32 36 
rnimr/irm v. 
Fig. 4. —Graph showing relation of temperature to the 
vegetative development of Gibberella saubinetii in 
artificial culture. The optimum temperature for 
growth, based on maximum diameter of colony, was 
a4 ° C. on unaddified agar and s8® on agar acidified 
with one drop of 35 per cent lacticadd per Petri-dish 
plate. 
INFLUENCE OF SOIL TEMPERATURE ON THE DEVELOPMENT OF MARQUIS 
WHEAT 
Uniform, plump kernels of Marquis wheat were selected for control and 
inoculated series alike, treated with mercuric-chlorid solution and sown 
in the soil temperature cans. The soil had been adjusted to the proper 
moisture content and placed in the cans several days previously. The 
wheat kernels were planted at a uniform depth of 1.5 inches, after which 
the cans were covered for 36 hours to prevent excessive evaporation from 
the soil surface. After uncovering and mulching, the containers were 
made up to their original weight each day throughout the duration of the 
