. 
14 MICROBES, FERMENTS, AND MOULDS. 
microbes, properly so called, are still often assigned to 
the class of fungi. We shall speak of them separately, 
and give our reasons for distinguishing them from 
true fungi. 
Hymenomycetes are the fungi which possess the 
hymenium or umbrella; all the edible species are 
included in this class, together with a great number 
of extremely poisonous species. They are generally 
of considerable size, and only a few among them are 
true parasites; they do not, therefore, enter into the 
plan of this work, and, in spite of the interest they 
present, we shall content ourselves with the brief 
notice of them we have just given. The other groups 
must, however, detain us longer. 
II. THE BAsIpIOMYCETES: UREDINEH, THE RUST OF 
WHEAT AND GRASSES. 
The name of cereal rust is given to a parasitic 
affection caused by a minute microscopic fungus which 
is developed on the leaves of wild and cultivated 
grasses. This rust appears in the form of orange 
patches, which gradually spread over the blades of 
wheat and other grasses, and its common name is 
due to this colour. Many of the plants belonging 
to other families are attacked by analogous parasites, 
and these fungi are all assigned by naturalists to 
the genus Uredo, and to the family of the Basidio- 
mycetes or Uredinew. 
