May 19,1923 
Relation of Soil Factors to Infection of Oats 
571 
ration. Low temperatures appeared to inhibit growth withoutj^causing 
any permanent injury to the fungus. Cultures were kept at the low 
temperatures in some cases for a period of four weeks or more, but no 
growth occurred. When these same cultures were transferred to warmer 
temperatures, growth soon was evident. 
Table I .—Effect of temperature on growth of Ustilago avenae in culture 
Average temperature. 
Amount oi growth. 
C. 
5 °. 
None. 
8 °. 
Very slight. 
14° . 
Slight. 
16^^. 
Fair. 
20° . 
Good. 
23° .*- 
Fair. 
28°. 
Slight. 
32° . 
Very slight (if any). 
36° . 
None. 
EFFECT OF TEMPERATURE ON GERMINATION OF SPORES AND PRODUCTION 
OF SPORIDIA 
The spores of Ustilago avenae placed in Van Tieghem cells in beef broth 
with a reaction of +10, Fuller's scale, germinated between 5° and 34° 
C., the minimum being between 4° and 5"^, the optimum between 15° 
and 28®, and the maximum between 31° and 34^ C. For sporidial pro¬ 
duction under the same conditions of culture as for spore germination 
the minimum and optimum are the same as for spore germination, but 
the maximum, 30®, is lower. 
THE EFFECT OF TEMPERATURE ON GERMINATION OF THE HOST, AVENA 
NUDA U. 
It is difficult to estimate the growth of the host as it is not easy to 
define a standard for growth. The plants in culture, i to 2 months old, 
appeared to be most vigorous where germination and growth of the 
seedlings had occurred at temperatures of 16° to 24® C. They elongated 
more rapidly at the higher temperatures but presented an etiolated 
appearance as compared with the healthy, stalky growth at the lower 
temperatures. The record is given in Table II. 
Table II. —Effect of temperature on germination of Avena nuda L, 
Average temperature. 
Observations on growth. 
C. 
. 
Germination but no subsequent growth. 
Germination but no subsequent growth. 
Germination with slight growth. 
Germination with slow growth. 
Secondary roots produced, plumule 1.3 cm. long. 
Optimum growth, plumule 3 cm. long. 
Good growth, plumule 2 cm. long. 
Less vigorous, plumule-i cm. long. 
5“ . 
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