So 
shown a remarkable uniformity in their capacity for infecting oat 
varieties over a period of years. 
Sorghum Smut Investigations 
Dr. D. Elizabeth Marcy continued investigations on the infec- 
tion of sorghum varieties with the covered and loose kernel smuts. 
Studies were made comparing the growth rates of uninoculated 
sorghum varieties before emergence from the sand. The suscepti- 
ble varieties were Dakota Amber Sorgo, Dawn Kafir, and Shallu, 
and the resistant varieties Feterita, Dwarf Yellow Milo and Darso. 
Marked differences were observed in the growth rate of the seed- 
lings. These varieties also varied in height at maturity, and the 
rate of growth of the seedlings corresponded to their relative 
heights. There was no indication of a correlation between sus- 
ceptibility and rate of growth of the seedlings. 
The influence of several different environal factors was studied. 
Experiments were carried out on the effect of the size of sand 
particles, the amount of moisture, the influence of sucrose dis- 
solved in water, and temperature. Seedling growth was found to 
be retarded by (1) maintenance of a low soil moisture (10 per 
cent. of the water-holding capacity) ; (2) moisture supplied as a 
2 per cent. sucrose solution; (3) low temperature; (4) very fine 
sand; and (5) heavy tamping of the sand in which the seeds were 
germinated. The combination of these conditions which retarded 
seedling growth proved very favorable to high percentages of in- 
fection in susceptible varieties. 
In other experiments, plants were stunted by removing part of 
the endosperm, with the purpose of determining whether this 
stunting would influence infection. In the series inoculated with 
the covered smut, a large number of the seedlings of the highly 
susceptible variety, Dakota Amber Sorgo, failed to survive. The 
amount of smut among those that did survive was less than for 
the non-stunted series. Since it is probable that those which died 
off were infected, no conclusions can be reached. Most of the 
— 
— 
plants of the somewhat less susceptible variety, Red Amber Sorgo, 
reached maturity, and the percentage of smutted plants was some- 
what greater in the endosperm-deficient series. The experiment 
was repeated, inoculating the seeds with the loose smut. Again, 
