The second group is by far the largest, most typical, and attractive in this family. It contains the black moulds and white moulds, technically known as the _Dematiei_ and the _Mucedines_. In the first, the threads are more or less corticated, that is, the stem has a distinct investing membrane, which peels off like a bark; and the threads, often also the spores, are dark-coloured, as if charred or scorched. In many cases, the spores are highly developed, large, multiseptate, and nucleate, and seldom are spores and threads colourless or of bright tints. In the _Mucedines_, on the contrary, the threads are never coated, seldom dingy, mostly white or of pure colours, and the spores have less a tendency to extra development or multiplex septation. In some genera, as in _Peronospora_ for instance,[P] a secondary fruit is produced in the form of resting spores from the mycelium; and these generate zoospores as well as the primary spores, similar to those common in _Algæ_. This latter genus is very destructive to growing plants, one species being the chief agent in the potato disease, and another no less destructive to crops of onions. The vine disease is produced by a species of _Oidium_, which is also classed with _Mucedines_, but which is really the conidiiferous form of _Erysiphe_. In other genera, the majority of species are developed on decaying plants, so that, with the exception of the two genera mentioned, the _Hyphomycetes_ exert a much less baneful influence on vegetation than the _Coniomycetes_. The last section, including the _Sepedoniei_, has been already cited as remarkable for the suppression of the threads, which are scarcely to be distinguished from the mycelium; the spores are profuse, nestling on the floccose mycelium; whilst in the _Trichodermacei_, the spores are invested by the threads, as if enclosed in a sort of false peridium. A summary of the characters of the family may therefore be thus briefly expressed:-- _Filamentous; fertile threads naked, for the most part free or loosely compacted, simple or branched, bearing the spores at their apices, rarely more closely packed, so as to form a distinct common stem_ = HYPHOMYCETES. [Illustration: FIG. 40.--_Rhopalomyces candidus._]