578 
Journal of Agricultural Research 
Vol. XXIV, No. 7 
produces its chlamydospores in the young ovaries. Many of these spores, 
when scattered, come in contact with the seed and the life cycle is 
repeated. 
REVIEW OF LITERATURE 
RECOGNITION OF THE RELATION OF CLIMATE TO THE SMUTS 
^e first recognition of a relation between environment and the de¬ 
velopment of the smuts of oats, or, in fact, of any closely related smut 
was made by Jones {15)- The observations recorded in that publica- 
uon indicated, in his opinion, that certain climatic conditions prevailed 
m Vermont which were especially unfavorable for the development of 
oat smut. In the following year, however, Jones (j6 ) found a higher 
percentage of smut ;n Vermont than in other sections of the country 
These observations were supplemented by the records, for one season, of 
the SOIL temperature during the period of germination and early develop¬ 
ment of the seedling. From these accumulated data, the writer con¬ 
cludes— 
it is evident that surrounding climatic or soil conditions may at any point in the con¬ 
test so favor one or the other of the contestants—either the oat plant or the smut fun¬ 
gus as to decide which shall come out victorious. 
ANALYSIS OF THE RELATION OF TEMPERATURE TO THE SMUTS 
Following Jones, other workers have recognized soil temperature as a 
factor of primary importance. Among them Hecke (12) distinguishes a 
tmeefold effect of temperature, involving particularly (i) the germina¬ 
tion of the spores and seeds, (2) the duration of conditions in host plant 
favorable for infection, and (3; the possibility of the fungus reaching the 
growing point of the plant. The greater number of the other publica¬ 
tions dealing with the relation of temperature to the disease can be 
classified according to the aspects thus distinguished. 
EFFECT OF TEMPERATURE UPON GERMINATION OF SPORES AND SEEDS 
{^3) found the cardinal points of temperature for spore ger- 
mination of Ustilago avetiae and of four other smuts to be as follows i 
Minimum between 5° and 11° C., optimum 22° to 30°, and maximum 
30° to 35°. 
Ravn (20) very early noted that the amount of oat smut varies with 
the time of sowing oats. Later, detailed experiments made possible the 
definite statement that the time of sowing affects greatly the occurrence 
of oat smut, that the quantity of smut is small or negligible when oats 
are sown early, and that it increases in later sowings. A decrease with 
very late sowing was observed in a few cases. In his discussion of the 
possible reasons for ^is climatic influence he presumes that the tem¬ 
perature during germination is the most important factor. 
Tubeuf (22), experimenting with the smut of oats, found no infection 
when the temperature was below 7° C. during the seedling stage and 20 
to 24 per cent at a temperature of 20"^ to 21°. In accounting for this 
difference; he showed that the minimum for the germination of the oat 
plant is lower than that of the smut, so that when the temperature is 
sufficiently low the host will escape infection. Thus, he is led to recom¬ 
mend early sowing. In a short paper, Appel and Gassner (r) make 
some general remarks on oat smut, which are essentially in agreement 
