"The smut 'berries,' or 'balls,' from an infected head contain millions
of minute bodies, the spores or 'seeds' of the smut fungus. These
reproduce the smut in somewhat the same way that a true seed develops
into a new plant. A single smut ball of average size contains a
sufficient number of spores to give one for each grain of wheat in five
or six bushels. It takes eight smut spores to equal the diameter of a
human hair. Normal wheat grains from an infected field may have so many
spores lodged on their surface as to give them a dark color, but other
grains which show no difference in color to the naked eye may still
contain a sufficient number of spores to produce a smutty crop if seed
treatment is not practised.

"When living smut spores are introduced into the soil with the seed
wheat, or exist in the soil in which smut-free wheat is sown, a certain
percentage of the wheat plants are likely to become infected. The smut
spore germinates and produces first a stage of the smut plant in the
soil. This first stage never infects a young seedling direct, but gives
rise to secondary spores, or sporida, from which infection threads may
arise and penetrate the shoot of a young seedling and reach the growing
point. Here the fungus threads keep pace with the growth of the plant
and reach maturity at or slightly before harvest-time.

"Since this disease is caused by an internal parasite, it is natural to
expect certain responses to its presence. It should be noted first that
the smut fungus is living at the expense of its host plant, the wheat,
and its effect on the host may be summarized as follows: The consumption
of food, the destruction of food in the sporulating process, and the
stimulating or retarding effect on normal physiological processes.

"Badly smutted plants remain in many cases under-size and produce fewer