10 BULLETIN" 1361, U. S. DEPARTMENT OF AGRICULTURE 
the fourth plat contained uninfested field soil obtained at Madi- 
son, Wis. In the autumn Harvest Queen wheat was sown in each 
plat. In the spring 95 per cent and 50 per cent of the plants 
in the infested Illinois and Indiana soils, respectively, developed 
rosette and mosaic. No mosaic or rosette developed in the steam - 
sterilized soil or in the Wisconsin soil. 
This experiment was repeated in 1923 and 1924, and while the 
percentage of diseased plants has varied a little from year to year 
the general results have always been the same. 
Each season since 1920 numerous experiments have been con- 
ducted with infested soil in small metal containers, and mosaic 
always has developed when susceptible varieties of wheat were sown 
and when the favorable environmental conditions were maintained. 
The disease has never developed in susceptible plants grown in unin- 
fested soil in containers adjacent to those in which mosaic-infected 
plants were growing in infested soil. 
Infested soil was transported to Alhambra, 111., in 1920 and to 
Arlington Experiment Farm, Va., in 1923. In both cases mosaic and 
rosette developed in plants grown in the infested soil, and no mosaic 
occurred in the plants grown in uninfested soil. 
While it would be possible to carry out elaborate experiments on 
the soil-transmission phase of this problem in insect-proof cages, it 
seems doubtful whether evidence so obtained would be more conclu- 
sive than that obtained by exposing all plants to the same degree of 
insect infestation, as was done in the experiments cited. In view of 
the evidence presented, it appears certain that the virus of wheat 
mosaic is carried in the soil. Whether it is held by the soil particles 
or by decayed plant tissue or whether it is contained in some soil- 
inhabiting and plant-infecting organism is not known. 
As yet there is no evidence indicating that wheat mosaic is trans- 
mitted through the seed. 
CONTROL MEASURES 
As shown in previous publications, 7 the control of rosette is 
effected by the use of resistant varieties. This applies likewise to 
the mosaic leaf mottling, as both rosette and the mosaic are phases 
of the same disease. Infested fields should not be sown to Harvest 
Queen, Missouri Bluestem, Nigger, Penquite (Penquite's Velvet 
Chaff), Brunswick, or certain selections of Fultz, Indiana Swamp, 
and Illini Chief. These varieties and selections are all very suscepti- 
ble to rosette as well as mosaic. Although the Currell variety does 
not develop rosette, it appears to be very susceptible to mosaic, and 
it should not be sown on infested soil. Most wheat varieties seem to 
be susceptible to mosaic, but in many cases the disease does not seem 
to be very severe. Selections have been made from Harvest Queen 
which apparently are immune from all phases of mosaic. These 
selections are being given further study. There is always the possi- 
bility of the resistant or apparently immune varieties serving as 
carriers. 
7 H. H. McKinney. Op. cit. 
R. W. Webb, and G. H. Dungan. Op. cit. 
R. W. Webb, C. E. Leigbty, G. H. Dungan, and J. B. Kendrick. Op. cit. 
