58 o 
Journal of Agricultural Research 
Vol. XXIV, No. 7 
there is no connection between the ability of the young plant to push 
toough the ground and the attack of smut. He considers the suscepti¬ 
bility of the host to be dependent upon internal chemical differences, 
and that the host is not affected by external conditions so as to permit 
the entrance or bring about exclusion of the smut. 
roSSIBI^E EFFECT OF TEMPERATURE ON THE ABILITY OF THE FUNGUS TO REACH 
THE GROWING POINT OP THE HOST AFTER PENETRATION 
Hecke’s third aspect, the possibility of the fungus reaching the growing 
point of the host plant, is difficult to distinguish from the second, the 
prolongation of the infection period. Investigators dealing with the 
disease do not know without studying the host and the fungus separately 
which of these is modified by the temperature factor. Hecke classes 
Brefeld’s (j) work under the third aspect in which the fungus is con¬ 
sidered modified. Using germinated oat smut spores as inoculum, with 
a lower temperature (one not over 7° C.) he obtained 40 to 46 per pent 
infection, whereas at a higher temperature (above 15® C.) he obtained 
27 to 30 per cent. With the factor of the germination of the smut spores 
eliminated, Hecke concluded that the fungus reached the growing point 
of the host more easily at the lower than at the higher temperature. 
From his results, Brefeld considers that if, in cultivation, the seeding is 
done in warm weather, followed by cold, more smut will develop than 
when the temperature remains constantly high. The use of germinated 
spores as inoculum makes it impossible to compare Brefeld’s work with 
that of other investigators of oat smut. 
RELATION OF MOISTURE TO THE SMUTS 
The relation of moisture is discussed by Clinton (4) and by Hungerford 
and Wade (74). The former notes greater loss from both loose and 
covered smut of oats in the “hardpan region” of Illinois than in central 
Illinois. He thinks that the higher moisture content of the soil in this 
region favors the fungus and causes more infection. The latter observed 
that in fields sown immediately after rain, a higher percentage of bunt 
appeared than in those sown under relatively dry conditions. Results 
obtained from their greenhouse experiments seemed to confirm this 
observation. 
EXPERIMENTAL STUDIES 
THE INFLUENCE OF TEMPERATURE ON SPORE GERMINATION 
The first problem was to redetermine the cardinal points of tempera¬ 
ture for spore germination. The spore material used was grown the 
spring previous to experimentation and was from 2 to 7 montibs old 
when used. To insure its uniformity, all the smutted heads were kept 
in one envelop, and the spores shaken from the heads were introduced 
into 30 cc. of medium in approximately the same quantities each time. 
After trying several different media, a beef broth (4 gm. Liebig beef 
extract and 10 gm. peptone per 1,000 cc. of distilled water) of -f 10 
Fuller’s scale (Ph6.i) was chosen. About two small loopfuls of the spore 
suspension were mounted in Van Tieghem cells or hollow-ground slides. 
As Duggar {6) has shown the form of 5 ie drop and the amount of evapor¬ 
ation to be significant, care was taken that all conditions of mounting 
