Aug. is, 1914 
Head Smut of Sorghum and Maize 
353 
Spores from Red Amber sorgo of the crop of 1911 were used in most 
cases. Before treatment they were thoroughly wet by shaking with dis¬ 
tilled water. The dirt and foreign material were removed by centrifug¬ 
ing, and later the single spores were separated from the spore balls 
by the same method. In Table II, Nos. 1 to 14 and 29 to 34, inclusive, 
separated spores were used, while spore balls were used for the other 
treatments, except the last two, which were mixed. With a wire loop 
the spores or spore balls were transferred from the wet mass at the bot¬ 
tom of the centrifuge tube to tubes of water, which were then placed in 
the thermal bath. At the end of the period of treatment a portion of the 
spores in suspension was poured or pipetted out of the tube into melted 
agar at 43 0 C., in which they were shaken up and were then poured into 
a Petri dish. This portion was incubated at 27 0 to 28° C. and was ex¬ 
amined from time to time under the microscope for germinating spores. 
Fig. 7. —Curves summarizing for different years the percentages of infection: First, in plantings of sorgo 
after all seed treatments; and, second, in control plantings. 
In the later treatments at 6o° C. (Table II, Nos. 29 to 34, inclusive) the 
spores were subjected to the hot-water bath in the tubes of melted agar, 
thus avoiding the subsequent transfer. The first method would appear 
to give more chance for error, and to this is due, perhaps, the slight sur¬ 
vival noted after rather severe treatments. 
In Table II it is seen that moist heat is fatal within the upper range 
of temperatures used in the seed treatments (see fig. 6), and even dry 
heat seems injurious to the spores of this smut (Table II, Nos. 35 and 36). 
The plantings from hot-water and modified hot-water treatments of the 
seed showed a field infection in no way correlated with the thermal 
death point of the spores. About 24,000 plants grown from seed treated 
according to the latter method showed an infection of 5.9 per cent as 
against 3.1 per cent in about 3,500 plants grown from untreated seed. 
Over 15,000 of the plants from treated seed were of the Red Amber sorgo 
variety, which showed 6.5 per cent of smutted plants as against 4.2 per 
cent in the controls. 
