468 * Journal of Agricultural Research voi. xxvn, n©. 7 
The optimum concentration for germination appeared to be between 
P H 5.1 and 5.7. In those concentrations in which only a few spores 
germinated—namely, P H 3.6 and P H 7.1—no sporidia were produced. 
These results correspond fairly closely to those which had been ob¬ 
tained previously when small quantities of young wheat-plant tissue 
were added to the solutions, although in these studies the procedure 
enabled the spores to germinate in solutions which were originally 
slightly more alkaline than those in which germination occurred in the 
present experiment. 
The previous treatment of the spores is thus an important factor in 
determining their subsequent behavior at germination. Hence, it 
might be expected that previous exposure to other environmental con¬ 
ditions might also have an effect on the nature and extent of germination 
in solutions of different hydrogen-ion concentration. 
The above results, however, indicate a set of conditions within which 
the spores of Urocystis tritici might be expected to germinate readily. 
There apparently is no information as to die behavior of the spores in 
relation to various conditions of soil acidity. Laboratory experiments 
thus merely indicate that a somewhat similar relationship might be 
expected to occur in the field. Other conditions being favorable, the 
spores germinate most readily when in contact with slightly acid solutions. 
VIABILITY OF SPORES 
It is not definitely known how long the spores of Urocystis tritici may 
retain their viability in the soil, although there is evidence that some spores 
may live for a considerable number of years. McDiarmid (jo) reports a 
case of infection in a crop after an interval of seven years. The seed 
was treated with formaldehyde solution and was sown on land which 
seven years previously had borne a diseased crop, but which had not 
been cropped since that time. Such evidence, of course, is far from 
conclusive, since there is a possibility that spores may have been blown 
on to the land in the meantime. McAlpine (29) reports some pot ex¬ 
periments in which he was unable to secure infection with spores that 
were more than 12 months old, although he does not consider these 
results as entirely conclusive. 
In experiments made by the writer it appeared that very few spores 
were viable after they had been kept 28 months in the laboratory. 
Repeated tests were made with spores which had been kept in the labo¬ 
ratory for periods ranging from three to nine years, but in no instance 
did any of the spores germinate. On the other hand, there is a general 
impression that the spores will retain their viability for several years. 
It thus appears that environmental conditions may have a very marked 
influence on the viability of the spores. 
Several investigators have studied the effect of controlled temperature 
and moisture conditions on the viability of the spores of a number of 
plant pathogenes. Recently Peltier (57) has observed that the viability 
of the urediniospores of Puccinia graminis tritici Form III is profoundly 
affected by the relative humidity and the temperature to which the 
spores are exposed. He found that the spores retained their viability 
longest within a range of medium relative humidities. 
In experiments on the viability of the spores of Urocystis tritici , the 
writer has used spores of different ages and from different sources, under 
controlled conditions of temperature and relative humidity. Relative 
