280 
Journal of Agricultural Research 
Vol. XXIX, No. 6 
tions at the time of inoculation might 
determine whether the spores would 
germinate immediately, or remain un¬ 
germinated behind the glumes. The 
age and condition of the spores might 
also be a determining factor. In our 
studies low percentages of infection 
were obtained by inoculating the 
flowers, and the stage the flowers were 
in when inoculated made little differ¬ 
ence in the amount of infection ob¬ 
tained. 
Hecke (9) illustrates a mycelium in 
the tissues of the scutellum of barley 
kernels. It does not seem entirely 
impossible that Hecke was mistaken in 
the identity of the fungus. On the 
other hand, it is possible that the fungus 
infects at flowering time to a certain 
extent. Certain local climatic condi¬ 
tions might be more conducive to floral 
infection. Should floral infection take 
place there still remains the possi¬ 
bility that the internal mycelium would 
not become active when the seed is 
sown. In this respect the control by 
superficial disinfection is significant. 
There may be specialized strains or 
races of the fungus Ustilago nuda such 
as have been found in other fungi, in¬ 
cluding some of the cereal smuts 
(6 and 17). This seems to be a very 
logical conclusion, in view of the fact 
that there is a recognized tendency on 
the part of living organisms to adjust 
themselves to their environment. In 
the higher plants not only varieties 
and strains but distinct individual 
differences within the variety or strain 
are found. It is not beyond possi¬ 
bility that there are strains of the loose- 
smut fungus which infect through the 
flower. 
Brioli (4), working with four varieties 
of barley, says that he found mycelium 
of Ustilago nuda in the scutellum of the 
seed of only one variety. He* was in¬ 
clined to the opinion that the other three 
varieties were resistant. The lack of 
infection might have been more nearly 
what happens in nature. However, 
the varietal differences of the host plant 
may be a determining factor. Some 
varieties may be more susceptible to 
this type of infection. 
The investigations recorded herein 
have shown that seedling infection by 
Ustilago nuda takes place abundantly in 
certain varieties of barley when the 
dehulled seed is inoculated. Infection 
is so heavy in many cases as severely to 
injure the young seedling. The rate 
of emergence of the seedlings from 
seed sown at different depths indicates 
the amount of injury done to the seed¬ 
lings. An injured seedling is more 
capable of emerging through thin than 
it is through thicker layers of soil 
within the depths at which sowing is 
customary. Loose soils are more favor¬ 
able to emergence than are close, com¬ 
pact soils. There may be a toxic effect 
of the fungus on the host but the 
data indicate that if a toxin exists it is 
produced internally after the plant is 
infected. There are no indications of 
injury due to the presence of spores on 
the seed. 
Seedlings of both susceptible and 
resistant barleys are injured by the 
fungus. Infection studies have shown 
that both types become infected. The 
germ tube is capable of penetrating 
directly the cell walls of the coleoptile 
and at least the first two leaves of the 
young seedlings. The surviving plants 
from inoculated seed produced a high 
percentage of heads smutted with loose- 
smut. Nakano Wase is an exception. 
It failed to become smutted in all 
experiments and apparently is highly 
resistant to invasion by the fungus 
after it enters the seedling. These 
investigations have shown conclusively 
that seedling infection by Ustilago nuda 
will take place in a number of varieties 
of barley and have shaken the long- 
accepted theory that floral infection is 
the only type of barley infection by 
the loose-smut fungus, U. nuda. 
SUMMARY 
Floral infection of barley by Ustilago 
nuda has been accepted as proved for 
many years. 
Surface disinfectants have been 
found to control loose-smut in certain 
varieties of barleys. 
Dehulled seed of a number of varie¬ 
ties of barleys inoculated with spores 
EXPLANATORY LEGEND FOR PLATE 8 
Effects of viable and devitalized spores of TJstilaqo nuda on Han River and Nakano Wase barley seedlings 
grown from hulled and dehulled seed sown 1^ inches deep ip flats in greenhouse, on Mar. 8, 1924. 
Han River: 
A. —Hulled, inoculated with viable spores; 96 per cent emergence. 
B. —Hulled, uninoculated; 93 per cent emergence. 
Nakano Wase: 
C—Dehulled, uninoculated; 86 per cent emergence. 
D. —Dehulled, inoculated with devitalized spores? 82 per cent emergence. 
E. —Dehulled, inoculated with viable spores; 32 per cent emergence. 
F. —Hulled, inoculated with devitalized spores; 90 per cent emergence. 
G. —Hulled, inoculated with viable spores; 92 per cent emergence. 
II.—Hulled, uninoculated; 92 per cent emergence. 
