May 19,1923 
Spore Germination of Ustilago Avenae 
589 
that the presence of oxygen entering the apparatus from any source 
might be detected. 
With the apparatus in this final arrangement, three spore suspensions 
were thus subjected to an atmosphere free from oxygen as determined by 
the analysis of the samples of air passing over them. In no case did 
these spores germinate. Control mounts in Van Tiegheili cells showed 
good germination. Before the apparatus was perfected and gas analysis 
made at the end of each germination, 15 trials had been made in which 
germination had occurred in only two instances when leaks in the ap¬ 
paratus, which admitted oxygen, were subsequently detected. The 
data confirm the results of the three final trials cited, and strengthen 
the evidence that Ustilago avenae spores will not germinate in the absence 
of oxygen. Some of these trials, however, have indicated that the spores 
will germinate in a low percentage of oxygen. In two experiments, ger¬ 
mination of 5.9 per cent was found when the oxygen percentage was 5.85 
and 1.95. The controls gave 28 and 35 per cent. In another trial in 
which germination was 27 per cent, and Ae control germinated 21 per 
cent, the gas analysis showed 0.5 per cent of oxygen. 
DISCUSSION AND CONCLUSIONS 
From the temperature experiments, it may be concluded that within 
the range from 9® to 28° C. there is no temperature effect upon the 
fungus which may prevent infection and establishment of the fungus 
within the host. According to Bartholomew and Jones (2) the range of 
temperature over which the highest percentages of smut occur is from 
12® to 28®. This is nearly covered by the optimum range for germination 
of the fungus, 15° to 28^. Here also, according to Haberlandt (< 9 , p- 43) y is 
included tiie optimum for the most favorable and rapid germination of 
the host; namely, 25° C. At 9®, where the percentage of smut is either 
zero or very low, it takes about 10 days for the host to appear above 
ground and from four to five days for a good germination of the fungus 
and subsequent sporidial production. It would seem that the lack of 
smut was in no way due to an unfavorable influence of temperature upon 
the fungus alone. At 29° and below 6® C., however, the temperature 
seems to be unfavorable to the fungus. At the first and above, the germi¬ 
nation is very much reduced and is abnormal, while sporidial production 
is rare. Here, it seems clear, a temperature effect may be the cause of the 
low percentage of smut. Below 6® it is possible that the host may 
develop before the germination of the fungus takes place, as the fungus 
requires about nine days to produce any considerable germination. 
These temperature conclusions are essentially in agreement with those 
of Ravn (20), Tubeuf (22), Eriksson (7), and Heald and Zundel (n). 
As Bartholomew and Jones (2) found a low percentage of smut at the 
high soil moistures, and as at 80 per cent soil moisture there is a decidedly 
low fungal germination, with a slight falling off at 60 per cent as compared 
with 30 per cent, it seems safe to conclude that at the high content of 
soil moisture the decrease in spore germination may be a direct cause of 
the low percentage of smut. Analyzing this still further, we can per¬ 
ceive indications that this may be due to a factor involving oxygen 
supply. Were thq oxygen completely eliminated at these high moisture 
contents, it could be stated conclusively that the absence of oxygen 
prevented the smut germination, for these experiments have demon¬ 
strated for this fungus the commonly assumed hypothesis that the spores 
