Order 2. =Rhizopaceæ.= _Rhizopus nigricans_ (_Mucor stolonifer_) which lives on decaying fruits containing sugar, on bread, etc., has, at the base of the sporangiophores, tufts of rhizoids, _i.e._ hyphæ, which function as organs of attachment. From these, “runners” are produced which in a similar manner develope sporangiophores and rhizoids. [Illustration: FIGS. 81, 82.--_Mucor mucedo_: _A-C_ stages in the formation of the zygote; D zygote; E germination of zygote: the exospore has burst, and the endospore grown into a hypha bearing a sporangium.] Order 3. =Thamnidiaceæ.= On the same sporangiophore, in addition to a large, terminal, many-spored sporangium, many smaller, lateral sporangia are formed with a few spores. Thamnidium. =B.= Asexual reproduction by sporangia and conidia. Order 4. =Choanephoraceæ.= _Choanephora_ with creeping endophytic mycelium, and perpendicular sporangiophores. Order 5. =Mortierellaceæ.= _Mortierella polycephala_ produces on the same mycelium conidia and sporangiophores. _M. rostafinskii_ has a long stalked sporangiophore, which is surrounded at its base by a covering of numerous felted hyphæ. [Illustration: FIG. 83.--_Pilobolus._ Mycelium (_a_, _a_), with a sporangiophore (_A_) and the fundament of another (_B_).] [Illustration: FIG. 84.--_Pilobolus._ Sporangium (_a″_) with stalk (_a-c_), which is covered by many small drops of water pressed out by turgescence.] =C.= Asexual reproduction only by conidia. Order 6. =Chætocladiaceæ.= The conidia are abstricted singly and acrogenously. _Chætocladium_ is a parasite on the larger Mucoraceæ. Order 7. =Piptocephalidaceæ.= The conidia are formed acrogenously and in a series, by transverse divisions. The zygospore arises at the summit of the conjugating hyphæ, which are curved so as to resemble a pair of tongs. _Piptocephalis_ and _Syncephalis_ live parasitically on the larger Mucoraceæ. Sub-Class 2. =Oomycetes.= Sexual reproduction is oogamous with the formation of brown, thick-walled _oospores_ which germinate after a period of rest. Asexual reproduction by conidia and _swarmspores_. Parasites, seldom saprophytes. The oospores are large spores which are formed from the egg-cell (oosphere) of the _oogonium_ (oosporangium, Fig. 89, 95). A branch of the mycelium attaches itself to the oogonium and forms at its apex the so-called “_antheridium_” (pollinodium[13]): this sends one or more slender prolongations (fertilising tubes) through the wall of the oogonium to the egg-cell.