Having thus disposed of the _Sporifera_, we must advert to the two families of _Sporidiifera_. As more closely related to the _Hyphomycetes_, the first of these to be noticed is the _Physomycetes_, in which there is no proper hymenium, and the threads proceeding from the mycelium bear vesicles containing an indefinite number of sporidia. The fertile threads are either free or only slightly felted. In the order _Antennariei_, the threads are black and moniliform, more or less felted, bearing irregular sporangia. A common fungus named _Zasmidium cellare_, found in cellars, and incrusting old wine bottles, as with a blackened felt, belongs to this order. The larger and more highly-developed order, _Mucorini_, differs in the threads, which are simple or branched, being free, erect, and bearing the sporangia at the tips of the thread, or branches. Some of the species bear great external resemblance to _Mucedines_ until the fruit is examined, when the fructifying heads, commonly globose or ovate, are found to be delicate transparent vesicles, enclosing a large number of minute sporidia; when mature, the sporangia burst and the sporidia are set free. In some species, it has long been known that a sort of conjugation takes place between opposite threads, which results in the formation of a sporangium.[Q] None of these species are destructive to vegetation, appearing only upon decaying, and not upon living, plants. A state approaching putrescence seems to be essential to their vigorous development. The following characters may be compared with those of the family preceding it:-- _Filamentous, threads free or only slightly felted, bearing vesicles, which contain indefinite sporidia_ = PHYSOMYCETES. [Illustration: FIG. 41.--_Mucor caninus._]