~1. Hymenomycetes~ (including the mushrooms, etc.). ~2. Hyphomycetes~ (moulds). ~3. Blastomycetes~ (yeasts and torulæ). ~4. Schizomycetes~ (bacteria). NOTE.--Formerly myxomycetes were included in the fungi; they are now recognized as belonging to the animal kingdom, and are termed "mycetozoa." ~MORPHOLOGY OF THE HYPHOMYCETES.~ At the commencement of his studies, the attention of the student is directed to the various non-pathogenic moulds and yeasts, not only that he may gain the necessary technique whilst handling cultivations of harmless organisms, but also because these very species are amongst the commonest of those that may accidentally contaminate his future preparations. The hyphomycetes are composed of a mycelium of short jointed rods or "hyphæ" springing from an axis or germinal tube which develops from the spore. Hyphæ are-- (a) Nutritive or submerged. (b) Reproductive or aerial. The protoplasm of these cells contains granules, pigment, oil globules, and sometimes crystals of calcium oxalate. ~Reproduction.~--Apical spore formation--asexual; zoospores--sexual. ~Mucorinæ.~--_Mucor_ (Fig. 77).--Note the branching filaments--"mycelium" (a), "hyphæ" (b). Note the asexual reproduction. 1. A filament grows upward. At its apex a septum forms, then a globular swelling appears--"sporagium" (d). This possesses a definite membrane. 2. From the septum grows a club-shaped mass of protoplasm--"columella" (c). [Illustration: FIG. 77.--Mucor mucedo.] [Illustration: FIG. 78.--Aspergillus] 3. The rest of the contained protoplasm breaks up into "swarm spores" (e). Finally the membrane ruptures and spores escape. ~Perisporaceæ.~--_Aspergillus_ (Fig. 78).--Note the branching filaments--"mycelium" (a). [Illustration: FIG. 79.--Penicillium.] Note the asexual reproduction. 1. A filament (b) grows upward, its termination becomes clubbed; on the clubbed extremity flask-shaped cells appear--"sterigmata" (c). 2. At free end of each sterigma is formed an oval body--a spore or "gonidium" (d), which, when ripe, is thrown off from the sterigma. Two or more gonidia may be supported upon each sterigma. _Penicillium_ (Fig. 79).--Note the branching filaments--"mycelium" (a) (frequently containing globules). Note the asexual reproduction. 1. A filament grows upward--"goniodophore" (b)--and its apex divides up into several branches--"basidia" (c). 2. At the apex of each basidium a flask-shaped cell, "sterigma" (d), appears. 3. At the apex of each sterigma appears a row of oval cells--"spores" or "conidia" (e). These, when ripe, are cast off from the sterigmata. [Illustration: FIG. 80.--Oïdium.] ~Ascomycetæ.~--_Oïdium_ (Fig. 80).--(This family is perhaps as nearly related to the blastomycetes as it is to the hyphomycetes.)