The _Physomycetes_ consist of two orders, _Antennariei_ and _Mucorini_, which differ from each other almost as much in habitat as in external appearance. The former, if represented by _Antennaria_, runs over the green and fading leaves of plants, forming a dense black stratum, like a congested layer of soot; or in _Zasmidium_, the common cellar fungus, runs over the walls, bottles, corks, and other substances, like a thick sooty felt. In the _Mucorini_, as in the _Mucedines_, there is usually less restriction to any special substance. _Mucor mucedo_ occurs on bread, paste, preserves, and various substances; other species of _Mucor_ seem to have a preference for dung, and some for decaying fungi, but rotting fruits are nearly sure to support one or other of the species. The two known species of the curious genus _Pilobolus_, as well as _Hydrophora_, are confined to dung. _Sporodinia_, _Syzygites_, &c., nourish on rotten Agarics, where they pass through their somewhat complicated existence. The _Ascomycetes_ contain an immense number of species, and in general terms we might say that they are found everywhere. The _Tuberacei_ are subterraneous, with a preference for calcareous districts. The _Perisporiacei_ are partly parasitical and partly not. The _Erysiphei_ include those of the former which flourish at the expense of the green parts of roses, hops, maples, poplars, peas, and many other plants, both in Europe and in North America, whilst in warmer latitudes the genus _Meliola_ appears to take their place.