The smut occurs in the smaller spikelets and completely destroys the ovaries, leaving only the outer wall. At maturity the ovary becomes considerably enlarged and the lower part is much darker in color. The wall of the spikelet breaks readily, exposing the spores to the air. The interior is filled with a mass of brown spores which are smooth, spherical to oblong, somewhat angular, from 6 to 8 u broad by 10 to 12 u long, but varying considerably in shape and size. These spores germinate readily in nutrient or lactose, or cane sugar solutions, or sterilized rain water. The spores in germination produce a slender, septate, promycelial tube with lateral sporidia. The sporidia enter probably at the time of the germination of the seed.