cluded
will remain unfermented for an indefinite time.

There has been much controversy as to the systematic position of the
yeast fungi, which has not yet been satisfactorily settled, the
question being whether they are to be regarded as independent plants
or only one stage in the life history of some higher fungi (possibly
the _Smuts_), which through cultivation have lost the power of
developing further.

CLASS I.--THE SMUTS (_Ustillagineae_).

The smuts are common and often very destructive parasitic fungi,
living entirely within the tissues of the higher plants. Owing to
this, as well as to the excessively small spores and difficulty in
germinating them, the plants are very difficult of study, except in a
general way, and we will content ourselves with a glance at one of the
common forms, the corn smut (_Ustillago maydis_). This familiar fungus
attacks Indian corn, forming its spores in enormous quantities in
various parts of the diseased plant, but particularly in the flowers
("tassel" and young ear).

The filaments, which resemble somewhat those of the white rusts,
penetrate all parts of the plant, and as the time approaches for the
formation of the spores, these branch extensively, and at the same
time become soft and mucilaginous (Fig. 38, _B_). The ends of these
short branches enlarge rapidly and become shut off by partitions,
and in each a globular spore (Fig. 38, _C_) is produced. The outer
wall is very dark-colored and provided with short spines. To study
the filaments and spore formation, very thin sections should be made
through the young kernels or other parts in the vicinity, before
they are noticeably distorted by the growth of the spore-bearing
filaments.

[Illustration: FIG. 38.--_A_, "tassel" of corn attacked by smut
(_Ustillago_). _B_, filaments of the fungus from a thin section of a
diseased grain, showing the beginning of the formation of the spores,
x 300. _C_, ripe spores, x 300.]

As the spores are forming, an abnormal growth is set up in the cells
of the part attacked, which in consequence becomes enormously enlarged
(Fig. 38, _A_), single grains sometimes growing as large as a walnut.
As the spores ripen, the affected parts, which are at first white,
become a livid gray, due to the black spores shining through the
overlying white tissues. Finally the masses of spores burst through
the overlying cells, appearing like masses of soot, whence the popular
name for