570 
Journal of Agricultural Research 
Vol. XXIV. No. 7 
water to loo gm. of dry soil, was discarded after trial because of the 
variation in soil-moisture conditions when soils of diiBferent water-holding 
capacities were used. The chief danger of the soil-saturation method lies 
in the unequal compacting of the soil but this error may be minimized 
by using a uniform method for handling all soil samples. 
The soil moistures were held constant by the use of galvanized con¬ 
tainers, insulated soil surfaces, and daily weighings for the determination 
of any moisture lost through evaporation. The soil reaction was deter¬ 
mined by the Truog® method and was found in all cases to be ‘‘medium 
acid.” The soil composition offered the greatest difficulties in the matter 
of uniformity, but these were overcome by securing soil from approxi¬ 
mately the same locality for all the series of experiments. It was a sandy 
loam with a water-holding capacity of 28 to 30 per cent for the first year's 
experiments and 39 to 41 per cent for those of the second year. Pure- 
line seed of the previous season was used, and sowings were made at a 
depth of I inch. The soil was thoroughly sifted, poured into the can, 
and tamped by dropping the can from a given height a uniform number 
of times, thus obtaining a fairly constant state of compactness. 
INFLUENCE OF TEMPERATURE ON GROWTH OF FUNGUS AND HOST 
The fungus, UstUago avenae (Pers.) Jens., was obtained from smutted 
heads of Avena nuda L. grown at Columbia, Mo., in the summer of 1918. 
This material was used for all of the inoculations during the winter and 
spring of 1918-19. Smutted heads obtained from our own plats of 
A, nuda L. in the summer of 1919 furnished the inoculum for the follow¬ 
ing year. Pure-line seed of A. nuda L., the hulless or naked oat, was 
chosen as the standard for experimentation because this species shows a 
high degree of susceptibility to loose smut. Uniform moistures were 
maintained throughout the infection period and for one week afterwards, 
following which the containers were removed from the tanks. The 
plants taken from the tanks during the colder months were allowed to 
mature in the containers in which they were growing, but those in the 
series removed from the tanks in the spring months were transplanted 
at once to open plats and allowed to mature out of doors. 
The study of the fungus in culture has been limited, but the results 
are clear cut. Potato-dextrose agar, with a reaction of +10 on the Fuller 
scale, was used. Agar sticks were melted, cooled, and heavily inocu¬ 
lated with sporidia from pure cultures of the fungus. These were poured 
into plates and allowed to incubate until many colonies appeared. 
Series of plates of the same medium then were inoculated by selecting 
uniform colonies and transplanting them. The single-spore method of 
culturing the organism was found impracticable because of the minute 
size of the spores, their tendency to cling together, and their poor germi¬ 
nation, even when incubated under optimum conditions. The results 
obtained are shown in Table I. 
When the cultures were removed from the Altmann incubators at the 
end of six days and allowed to remain at room temperature, growth 
occmred in all except those which had been exposed to 36° C. Growth, 
however, was very slight in cultures taken from 32°, showing that only 
a small percentage of the sporidia were able to survive exposure to this 
temperature. This was not due to desiccation of the medium, because 
sufficiently high humidity was maintained to prevent undesirable evapo- 
Truog, E. a new test for son. AaniTV. Wis. Agr. Exp. Sta. Bui. 249,16 p., 3 fig., 1 col. chart. 1915. 
