PHYCOMYCETES. (a) OOMYCETES 423 



free spermatozoids, but transfers a single gamete by a tube, as in the 

 higher land-living Plants. The oogonium retains its character as in 

 Vaucheria. All these presumed changes are biologically likely to occur. 

 Such considerations justify the recognition of Fungi included among 

 the Oosporeae as of probable Siphonaceous origin, from types already 

 advanced in their sexuality as far as Vaucheria is. 



' 



PHYCOMYCETES. (b) ZYGOMYCETES. 

 THE MUCORS. 



The Zygomycetes include many common Moulds. They are mostly 

 saprophytes, though some of them are parasites not only on other 

 plants and animals, but even on one another. They are characterised 

 first by their coarse non-septate hyphae, but more particularly 

 by the manner of their sexual reproduction, which results from 

 the fusion of two similar, multinucleate branch-endings, to form a 

 single large resting-spore, or zygo-spore. The chief representatives 

 are the Mucors (Mucorineae) found on decaying organic matter in 

 moist circumstances. If moist bread, horse-dung, brewer's grains, 

 or other organic substances be kept warm for a day or two under 

 a bell-glass, Mucorineous Moulds will almost certainly appear. They 

 are often of considerable stature. Phycomyces nitens, which comes 

 commonly on brewer's grains, may be several inches in height, the 

 coarse sporangiophores ending in sporangia easily seen with the 

 naked eye. 



Another common type is Empusa muscae (Entomophthorineae), 

 which lives parasitically on the House Fly. In autumn the infected 

 flies become sluggish, and finally resting on a windowpane, or elsewhere, 

 they appear as though surrounded by a white halo. This is formed 

 by the conidia thrown off to a distance by the conidiophores, which 

 project from the body of the fly killed by the fungus in its vegetative 

 stage. Thus, while most of the Fungi of this group are saprophytes, 

 some may be parasitic, even on animals. 



If the sporangiophores of Mucor or Phycomyces be followed to their 

 base, they are found to arise from finer filaments forming a profusely 

 branched mycelium, which traverses the substratum. A good idea 

 of its nature is obtained by culture from the spore on a glass surface 

 (Fig. 359). It is then seen how, starting from the spore as a centre, 

 the mycelium may radiate outwards, with successively finer branches 

 of its non-septate tubes. Each of the thick upright sporangiophores 



