MILDEWS, RUSTS AND SMUTS 
187 
UROCYSTIS 
Distinguished at once from every other genus, by the 
dark-coloured fertile spores of the spore-balls being 
surrounded by very pale, sterile cells. 
USTILAGO, Pers. 
Vegetative mycelium permeating the tissues of the 
host-plant, soon disappearing, spore-producing mycelium 
branched, becoming swollen and gelatinous, spores pro¬ 
duced in rows in the tufted terminal branchlets, and forming 
a black, powdery mass at maturity ; promycelium short, 
usually septate, bearing laterally, less frequently terminal, 
minute promycelium spores. 
Many species form long, dark streaks on leaves and 
stems, others develop in anthers, others again in the ovary. 
In some forms there is a hibernating mycelium present in 
some permanent part of the host-plant, root, bulb, etc., 
which grows up yearly with the plant ; such plants are 
diseased every season without being infected anew. 
Many species prove very destructive to cereals, and from 
their very conspicuous appearance, more especially when the 
ears are attacked, and reduced to a black sooty-looking mass 
have received popular names, as " smut ” and " slean.” . 
The bulk of species are parasitic upon either grasses or 
sedges, and when other groups of plants are attacked, a 
preference is shown for monocotyledons. Much work 
yet remains to be done before the true limits of our so- 
called species are clearly defined. Infection experiments 
alone can lead to this end. Some species can only infect 
the host-plant during its earliest seedling stage, others are 
infected during the flowering stage, hence no one preventive 
method will meet all cases. Where the seedling is in¬ 
fected, as in the case of oats, the spores adhering to the 
husk of the oats, when so^vn, germinate at the same time 
as the oat seedling, which becomes infected in the ground, 
the mycelium growing along with the oat plant, and finally 
producing its spores in the grain. In this case, if the 
oat seed is properly treated, so as to destroy all spores 
adhering to its surface, before sowing, the disease is checked. 
When the flower or foliage is the portion infected, the 
removal of diseased plants, cultivated or wild, that would 
furnish spores, should be attended to. In those cases 
where there is a perennial mycelium in the host-plant, 
no part of such, though apparently free from disease, 
should be used for propagation. 
