47 
former being very susceptible to it, regularly giving 100 per cent. 
infection. Scottish Chief, however, is only moderately suscepti- 
ble; while some plants are infected in each experiment, 100 per 
cent. infection is practically never obtained. 
Two races of covered smut were used. The Missouri race was 
used to inoculate Monarch, which is completely susceptible, and 
Danish Island, which usually gives only a small number of in- 
fected plants. The Fulghum race of covered smut 1s charac- 
terized by its ability to infect Fulghum, a variety of the red oat 
group, and also Black Mesdag, a variety extremely resistant to all 
other known races of smut. Only rarely does either of these 
varieties give 100 per cent. infection, 
Three different sets of experiments were carried out. 
1. The influence of length of day and sodium nitrate on the 
growth of the host and the development of the smut mycelium 
was tested. There were grown four sets of cultures, two being 
supplied with sodium nitrate and two without. The experiments 
were started about the middle of January and continued until all 
the plants had headed out. One set of cultures was illuminated 
for additional hours in the late afternoon and the other was grown 
without artificial light. 
There were marked differences in the time required for the 
plants to reach the stage of heading, when the presence or absence 
of infection is readily determined, since the flower parts are com- 
pletely replaced with the smut spores. The illuminated plants 
tout nitrate grew rapidly, heading in about ten weeks, but 
ied 
— 
wit 
showed practically no stooling. The illuminated plants supp 
with nitrate headed a few days later. They were taller and stooled 
out to some extent. It was several days later before the non- 
illuminated cultures headed out, the ones without nitrate being 
slightly earlier. The cultures of these plants were much taller and 
stooled out more than those of the illuminated series, the plants 
supplied with sodium nitrate especially producing a very rank and 
— 
abundant growth. 
2. Another series of cultures was grown in a comparatively 
poor soil to which various chemicals were added. To one set of 
pots a full nutrient solution, including nitrate, potash and phos- 
phate, was supplied. In comparative series, there was a deficiency 
