Order 2. Perisporiaceæ, Moulds and Mildews. A group of Fungi widely distributed and found in all situations. Usually they have a well-developed surface mycelium, and small, round, seldom conspicuous ascocarps, containing ovoid, pulley-like spores. They are partly saprophytic, partly parasitic, in the latter condition having a brown mycelium.
Fig. 110.—Eurotium glaucum: a longitudinal section of a half-ripe ascocarp, bounded externally by a well-defined layer of cells, enclosing asci in various stages of development; b a semi-ripe, c an almost ripe ascus; d and e spores seen from the edge and side; f germinating spore twenty-two hours after been sown in plum juice.
Eurotium glaucum (= E. herbariorum, Figs. [109], [110]) and E. repens live on dead organic matter, preserved fruits, etc. The conidial forms of both species are known as “Moulds” (Fig. [109]), and formerly were described under the name “Aspergillus glaucus.” The conidia for some time remain attached to each other in chains (Fig. [109] a); they are abstricted from sterigmata arranged radially on the spherical, swollen end of the conidiophore. The small yellow or brownish ascocarps are frequently found in herbaria, especially when the specimens have been insufficiently dried. Aspergillus fumigatus and others are pathogenic, causing mycosis in warm-blooded animals.
Fig. 111.—Penicillium crustaceum: a conidia (× 300); b germination of conidia; c small portion of mycelium, produced from a conidium at *, with five conidiophores; d young conidiophore (× 630), a flask-shaped cell is abstricting a conidium; e the same conidiophore after 9–10 hours.
Fig. 112.—Penicillium crustaceum: a two spirally-coiled hyphæ arise from the mycelium, from one of which (archicarp) the asci are produced; b a further step in the development of the ascocarp; the branching archicarp is surrounded by sterile hyphæ; c section of young ascocarp; the larger hyphæ in the centre are the ascogenous hyphæ; these are enclosed by a pseudo-parenchyma of sterile hyphæ (× 300); d series of ripe asci with spores; e four ascopores seen laterally; f germinating ascospores (× 800).
Penicillium crustaceum (P. glaucum, Figs. [111], [112]) is an exceedingly common “Mould.” Its mycelium appears very frequently on any organic matter which is permitted to remain untouched, and soon covers it with a dense mass of blue-green conidiophores. These branch at their summits and bear flask-shaped cells from which the conidia are abstricted. The ascocarps which, both in size and colour, resemble grains of sand, have only been obtained in luxuriant cultivation with a limited supply of oxygen.
Capnodium salicinum (Fumago salicina, Cladosporium fumago), a common Mildew, forms dark overgrowths on the leaves and branches of various shrubs (Poplars, Elms, Willows) and on Hops. The conidia appear in various forms, as on conidiophores, in conidiocarps with large multicellular conidia, and in conidiocarps with small unicellular conidia; in nutritive solutions yeast-like conidia are also developed.—Apiosporium pinophilum produces mildew on the leaves of Abies alba and Picea excelsa. (The conidial-forms were formerly described as “Antennaria pinophila”).