648 
The Smut of Onions. 
It was probably observed first in Connecticut about 1860, since which 
time it has spread very rapidly, and has also been noticed and 
described by botanists both in the United States and in Europe. 
As to its previous history there is much uncertainty, as the fungus 
has not, up to the present, been found on any wild species of Album, 
the genus of which (the onion) Allium Cepa, is a member. 
The smut of the ctiltivated onion belongs to the same group of 
fungi as that which includes the bunt of wheat {Tilletia Caries, Tul.) 
and the smut of oats and barley (Ustilago carbo, Tul.) It appears 
on the seedling, first in the form of dark spots at different heights 
in the leaves, and commonly this occurs just below the knee ; later, 
longitudinal cracks form at one side of the spots, and this part of 
the leaf is observed to have become a dry fibrous mass covered 
with a black sooty powder. Occasionally only the first leaf is 
attacked, and falls, when the plant may recover and come to matu- 
rity ; but more frequently, as the leaves appear one after another 
above ground, they are found to be affected in like manner to the 
first, and if the plant be strong enough to resist the attack suffi- 
ciently it may grow to a considerable size, and survive untH the 
time of harvesting. It will then be found, on pulling it up, that 
not only has the disease attacked the leaves, but that the bulb also 
has become more or less covered by black elevations running down 
to its base. Such onions either dry up, or rot, soon after being 
pulled. The black, smutty powder which thus forms on the leaves 
and btilb consists of the spores of the fungus. Like the spores 
of bunt and of smut of oats they are very minute, and do not measure 
more than ^ ^ ,^ g ^ ^ of an inch in diameter. 
In the more familiar cases of bunt and smut of our cereal crops 
the disease is propagated by the spores adhering to seed (see ToL 
xxiv. Second Series, page 397), whereas the spores which may become 
distributed on the ground appear to have no further effect on crops 
sown on that ground. The smut of onions, on the contrary, appears 
to retain its power of attacking a second crop after being left in the 
ground by a first, and Dr. Thaxter is of opinion that the risk of the 
spores being carried on the seed is comparatively small. Experi- 
ments, indeed, which were made by him render it extremely probable 
that this is the case, and he recommends farmers to keep their 
agricultural implements very clean when used for tilling onion land, 
in order to prevent the spores from being carried from one' piece of 
land to another. 
How long the spores of the onion smut may remain dormant in 
the earth depends, no doubt, on the conditions of temperature and 
moisture in which they are placed, but it appears from the e\-idence 
which Dr. Thaxter has collected that this may be certainly more 
than five years. 
The young onion plant is attacked almost as soon as the seed ger- 
minates, and consequently, when considering the best way in which 
to apply a series of fungicides, the investigator was led to the con- 
clusion that to dress the seeds would be of no use, and that the only 
method would be to ensure their operation just at the time when the 
