74 Smuts [cH. 
If grains of oats taken from a badly smutted field 
are sown, some of the resulting plants will be smutted 
and others quite clean. At the various stages of 
growth very little difference is noticeable between the 
plants which will produce healthy and those which 
will give smutted grain until well on towards harvest. 
The infected plants are said to be more robust and 
usually taller. When the grains are beginning to 
form some of the ears show a darker appearance, and 
as they ripen become blacker until a stage is reached 
when the ears seem to be making soot instead of 
grain (see Fig. 25). 
In looking for a suitable means of dealing with 
the smuts it is very important to know how the 
plant is first attacked. Barley, oats, and wheat show 
differences in this respect. 
When infection 
Host. Fungus. Common name. takes place. 
A. Barley Ustilago hordei | Covered smut of barley 
( 5 avenae Loose smut of oats ...| At seedling 
Oats  . ,, levis or Covered smut of oats ... period. 
kolleri : 
B. Barley  Ustilago nuda Loose smut of barley ... | At flowering 
Wheat ; tritict Loose smut of wheat ... } period. 
These fungi are very similar in structure and at 
one time were considered to be the same. Experiments 
have shown that under no circumstances can either 
produce any of the others, thus indicating that they 
are all distinct forms. 
Loose smut can easily be distinguished from covered 
smut as its spores come out of the grain and often 
leave the stem of the ears bare, whereas in covered 
smuts the spores remain in the grain on the ears. 
