472 
Journal of Agricultural Research voi. xxvii, No. 7 
under Australian conditions. If the spores germinated readily, it would 
be a simpler matter to free the soil of viable inoculum merely by rotation 
of crops, and control would be largely a question of seed disinfection. 
At present, however, under Australian conditions, the inoculum in the 
soil appears to be the major source of infection. 
RELATION TO MOISTURE 
It is generally conceded in cases of soil infestation by cereal smut 
organisms, other factors being favorable, that there is a fairly close 
correlation between the amount of smut in the crop and the amount of 
moisture present in the soil during the period prior to sowing. 
McAlpine (29), in flag-smut infection experiments, reports that sowings 
made in dry, infested soil resulted in 14 per cent of infection when germi¬ 
nation of seed of wheat and fungous spores occurred simultaneously, 
immediately following the first rains. When sowings were made on 
adjacent plots one month after rain, only 1 per cent of the plants became 
infected. 
Heald and Woolman ( 16 ), in discussing the relation of moisture to 
infection of wheat by bunt, state that sowing in dry soil and waiting for 
rain is better than sowing in a very wet soil. Mackie (31) also observed 
that there may be sufficient moisture in a soil for germination of wheat 
seed and yet be insufficient for germination of the bunt spores. Hunger- 
ford ( 20 ), in studies on the same disease, reports that there is a very 
definite relationship between the amount of moisture at seeding time and 
the amount of bunt in the resulting crop of wheat. A high soil mois¬ 
ture content at planting was conducive to heavy infection. These 
authors agree that very little infection results if sowing is delayed for 
some weeks after the incidence of heavy rains. The spores of Tilletia 
tritici rapidly lose their power to infect, particularly if the soil is 
cultivated frequently. 
Jones (22) records that the spores of Ustilago avenae (Pers.) Jens, do 
not germinate readily in very moist soils. She states, “Germination 
percentages were greatly reduced at 80 per cent of the water-holding 
capacity.” 
Walker and Jones (32) have shown that soil moisture is not a limiting 
factor in the development of the onion-smut fungus, Urocystis cepulae 
Frost. They state that “a high percentage of infected plants resulted 
over the entire range in which good germination and growth of the host 
occurred.” 
In greenhouse experiments with spores of Urocystis tritici , the writer 
has observed that wheat plants may become infected when seed is sown 
in infested soil which had been watered constantly for five weeks. The 
writer has shown in a previous paper ( 3 5) that the moist spores rapidly 
lose their viability when subjected to a temperature of 27.5 0 C. for a few 
hours. Spores which had been presoaked in distilled water for five 
days at 20° failed to germinate after exposure for 36 hours at 27.5 0 . 
There are thus two possible reasons for reduction of amount of viable 
inoculum in moist soil: (1) The spores may germinate and perish in the 
absence of a suitable host and (2) they may lose their capacity for ger¬ 
mination. 
It has been mentioned above that the spores of Urocystis tritici will 
produce sporidia either in moist air or when totally submerged in 
water. It is possible that there are certain limits of soil moisture 
