Feb. 16, 1924 
Flag Smut of Wheat 
477 
distribution of the pathogens within the host 
The distribution of the pathogene within the host has been studied by 
investigators of other smuts. 
McAlpine (29) cites an instance in which a barley plant produced heads 
affected with loose smut, Ustilago nuda (Jens.) Kell, and Sw., early in the 
season. These heads were cut back and a second series of culms was 
produced. All of these were infected. 
Potter (38) also has discussed the phenomenon of infection of the nodal 
branches of sorghum by Sorosporium reilianum (Kuehn) Me Alp. He 
examined the buds on individual culms for presence of the parasite. In 
some cases the basal portion of the culm escaped, and occasionally the 
top grew away from the parasite, although, in this instance, it usually 
remained sterile. The regularities in infection of these buds indicated 
that they were infected early, rather than that primary infection occurred. 
Potter states that the extent to which the mycelium develops during the 
first few weeks while the sorghum plant is growing slowly determines 
the final extent of infection. 
Histological studies of the tissues of plants infected with flag smut 
indicate that the mycelium is frequently observed at the nodes even when t 
the main shoot is of considerable length (fig. 1, d, and PI. 3, D, a). 
In tests on partially infected plants in the soil-temperature series, all 
infected culms were removed, and it was observed that the new culms 
which subsequently developed were most frequently infected. In other 
instances infected shoots were observed to arise from nodes almost 2 
inches from the level of the ground and on main stems otherwise showing 
no sign of infection. 
From the above it would appear that those conditions which favor the 
development of secondary culms might very readily result in an increase 
in the amount of damage resulting from flag smut. 
It is possible that the relatively crowded condition of the plants in the 
soil temperature containers was sometimes unfavorable to the produc¬ 
tion of tillers. Several plants, consisting of a single stem only, produced 
normal heads and thus did not have as full an opportunity of indicating 
the presence of the parasite as did those plants which produced secondary 
shoots. 
Hecke (17) has described a form of infection which he terms “Trieb- 
infektion.” He claims to have produced infection of the young shoots 
of Melandryum by cutting back 2-year-old plants and dusting the crown 
with spores of Ustilago violacea (Pers.) Fuckel. Subsequent shoots were 
smutted. A similar experiment was conducted with the perennial rye, 
Secale montanum. The plants were cut back to the crown and dusted 
with spores of Urocystis occulta (Wal.) Rab. The shoots which subse¬ 
quently developed were affected with smut. Hecke suggests that this 
mode of infection is not restricted to these organisms but that it occurs 
with other smut fungi. 
An unsuccessful attempt was made by the writer to produce flag smut 
in wheat by a similar method. Twenty-four plants of Federation wheat 
were cut back to within one-fourth of an inch of the ground level, the 
soil was removed from the crown and the upper roots, and the plants 
were heavily inoculated with spores of Urocystis tritici. Soil then was 
added to cover the plants completely, but the smut did not appear in 
any of the young shoots which subsequently developed. It is possible 
that the results were negative because few spores germinated. More 
