SORGHUM SMUTS AND VARIETAL RESISTANCE 9 
affected the ears also generally are smutted and destroyed, but 
occasionally one will escape or be only partially attacked. On the 
other hand, the tassel may escape when the ear is destroyed. The 
smutted plants frequently are stunted and remain green somewhat 
longer than normal plants. The smut masses are inclosed in a 
delicate pinkish white membrane which ruptures at maturity, expos- 
ing the spores. In large sori the fibro vascular tissues of the host 
(PL IX) persist, surrounded by the spores. 
The spores are united into spore balls, firm at first but later readily 
breaking up. These are dark brown in color, globose to oval or 
irregular in form, and 80 to 112 /x in length. The spores are globose 
to subglobose or somewhat angular, minutely but densely verruculose, 
and from 10 to 13 /jl in diameter. 
The germination of the spores has been studied by Brefeld (10), 
Norton (80), McAlpine (70) , Potter (90), Kulkarni (63), and Butler 
(21). Some of these investigators seem to have had no special 
difficulty in obtaining germination in water or nutrient solutions. 
On the other hand, Kulkarni and the writers of this bulletin had 
great difficulty in getting successful results. Potter (90) was seldom 
able to obtain more than 15 per cent germination in water. 
On germination a promycenum is produced, usually four celled, 
sometimes branched, with sporidia occurring terminally and later- 
ally. In a nutrient solution the sporidia bud abundantly, forming a 
large number of secondary sporiclia. 
Several investigators have attempted to produce artificial infection 
by contaminating the seed or soil at seeding time. Brefeld (10) 
reports that Kuhn succeeded in producing infection with this smut 
and also Ustilago cruenta in the same plant. Passerini (83) states 
that he was able to infect maize but not sorghum, using spores col- 
lected on maize. Kellerman (54) attempted a number of inoculation 
experiments with head smut. He obtained two infected plants in 
his greenhouse inoculations. He also inoculated a number of varie- 
ties of maize in the field but obtained only two infected plants of 
pop corn. In another experiment (55) he succeeded in infecting 
three plants of sweet corn, having inoculated varieties of field corn, 
sweet corn, pop corn, and sorghum. Kellerman and Jennings (56) 
report practically complete failure in their inoculation experiments 
with varieties of dent corn, pop corn, sweet corn, and sorghum, ob- 
taining only one smutted pop-corn plant. Clinton (23) failed to 
obtain infection by inoculating seed and seedlings. Hori (49) also 
reports negative results from his inoculation experiments. McAlpine 
(70) produced infection in a single maize plant by seed inoculation. 
Potter (90) recently made an extensive study of this smut. He 
conducted field experiments at four different stations, Amarillo and 
Chillicothe, Tex., St. Paul, Minn., and Rosslyn (Arlington Experi- 
ment Farm), Va. By using inoculated seed during three years he 
was able to obtain infection only at Amarillo and Chillicothe; and 
he came to the conclusion that seed-borne spores are negligible in 
causing infection, which, instead, takes place from spores present in 
the soil. The fact that the spores do not germinate readily in water 
or culture solutions used lends further support to this view. It 
would seem that the spores may retain their viability in the soil 
108(539°— 25f 2 
