Volume 6

The natural history of plants : their forms, growth, reproduction, and distribution / from the German of Anton Kerner von Marilaun ; translated and edited by F.W. Oliver, with the assistance of Marian Busk and Mary F. Ewart ; with about 2000 original woodcut illustrations and sixteen plates in colours.

  • Kerner von Marilaun, Anton, 1831-1898.
Date:
1897
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    able to remain dormant over long periods. Aspergillus is sometimes parasitic, and is stated to promote a diseased condition of animal tissues known as mycosis. A. fumigatus is found growing spontaneously in the air-passages of birds and in the human lungs. Tuheracece.—These are subterranean saprophytes whose mycelia grow in humus. Their fructifications are solid, tuber-like bodies of various sizes. The Trufiles {Tuber rufum, T. melanosporum, T. cestivum, &c.) are well-known, and several of the species are esteemed as delicacies. In section the Truffle-fruit shows a curious mottled appearance due to its irregular chambered character. The chambers are filled with hyphae which produce numerous oval asci, each containing 4 spores (c/. fig. 387 \ which represents an enlarged chamber); the spores are covered with delicate spines. The wall of the fructification consists of a hard parenchyma-like layer, and possesses a rough and warted exterior. As the fructification ripens the mycelium disappears, the Truffles being found detached in the soil. The spores are ultimately liberated by the decay of the fruit. Elaphomyces produces fruits about the size of a nut. The mycelium of species of this genus is concerned in the for- mation of the fungal investment or mantle of the roots of Pine-trees known as mycorhiza (c/. vol. i. pp. 249, 250); in the Amentacese, &c., neither the species nor group to which the Fungi forming this mantle belong has been ascertained. Pyrenomycetes.—An extremely large and varied group, including both parasitic and saprophytic forms. The essential character of the family is the presence of flask-shaped chambers with a pore at the apex in which the asci are produced. The chambers, the perithecia, may be either solitary upon the mycelium in the simpler forms or embedded in receptacles of most varied form (the stromata) in the more complex. Sections of perithecia are shown in figs. 385 ® and 386 A great many Pyrenomycetes possess conidial as well as ascus - fructifications. The conidia may arise in tufts from the surface of the mycelium or in urn-shaped cavities—not unlike perithecia—which have been termed pycnidia. As a rule, the conidial pre- cedes the ascal stage. This variety in fruiting has led to the recognition of several forms, which are only stages in the life-history of one Fungus. Consequently, as knowledge extends, many of these supposed species have to be suppressed. Among the simpler forms may be mentioned Podospora, which produces solitary sessile perithecia upon its mycelium. Polystigma rubrum, which occurs on the leaves of species of Cherry and Plum, produces a brilliant red spotting on the leaves. The mycelium permeates the internal tissues, and during the summer the conidial receptacles or pycnidia are formed. Later, usually in the following spring, in the fallen leaves, the perithecia arise, and the ascospores now liberated infect the young foliage in the vicinity. Nectria cinnabarina, another fairly simple form, occurs as little red cushions on the branches of Horse-Chestnut, Elm, Sycamore, &c.; these cushions burst through the bark budding off conidia (this is the bright red stage), whilst later, as tiny lobes, the perithecia arise upon them, each lobe containing a single perithecium (this is the dull crimson stage). The number of simple parasitic Pyrenomycetes is almost endless.
    1 Conlyceps Taylori, a pyrenomycetous Furgu which attacks caterpillars; the branched antler-like stroma has developed Irom the sclerotlum, and its lower waited portion bears the perithecia. '■> Three perithecia; enlarged. 3 a perithecium ^ in section. * Two asci containing filamentous spores, s Vertical section of a perithecium of Xylaria Hypoxylon. « Ascus of same, f Mycelium of Eurotium bearing a couidial hypha (to right, above), a commencing fruit (to left), and a ripe ascus-fruit (to right, below). « A conidium of the same being abstricted. 9 Entangled hyphae from which a fruit arises; the spiral central hypha has been interpreted as a female organ, the tubes growing up the side as male. 1° A young fruit of the same in section; the asci arise later from the large coiled central hypha. A single ascus of Eurotium. tnat. size; 3,8, 5x50-90. 5,6x500; ^xlOO: 8-iix250.
    Of complex forms with stromata we may mention Cordyceps, Xylaria, and Glaviceps. Cordyceps militaris and other species attack caterpillars. The germ- tube having once effected an entrance into the body of the caterpillar and estab- lished itself in the superficial layers begins to sprout vigorously, these sprouts being carried in the blood to all parts of the body. The sprouts now grow into hyphae, and gradually the whole caterpillar is replaced by a dense fungal tissue which 4 Fig. 386.—The Ergot of Rye, Claviceps purpurea. 1 Ear of Eye showing two sclerotia of the Fungus. 2 Conidia arising from the mycelium which develops around the ovary. * Stalked stromata arising from the sclerotium. * Longitudinal section through the head of a stroma showing the peri- thecia at the edge. 6 Vertical section through two perithecia showing the asci. « Asci. ? Ascus liberating its filamentous spores. 8 Filamentous spores. nat. size; 2x200; *X40; 8x60; • and ^xVOO; 8x760. (Partly after Tulasne.) maintains outwardly the form and appearance of the caterpillar, although of animal substance but little traces are left. This fungal mass is known as a sclerotium, and it can remain dormant for seme time. Ultimately a branching stroma arises from the sclerotium {Cordyceps Taylori, fig. 385 p. 679), or, in C. militaris, several club- shaped stromata. These remarkable stromata are covered with little papillae on their lower portion, and each of these papillae corresponds to a perithecium (figs. 385 ^ and 385 ®). The spores in the asci are long and slender (c/. fig. 385 *). A
    Pyrenomycete which produces an antler-like stroma resembling that of Cordyceps Taylori, and which is exceedingly common on old tree stumps, is Xylaria Hypoxylon. Indeed, the stroma represented in fig. 385 ^ would almost do for that of this Xylaria. It is purplish in colour below where the perithecia are borne; at the tips it passes over into a glaucous grey colour, this bloom being due to the conidia, which are abstricted in this region. Another curious fingered species, X. polymorpha, is also met with in similar situations. Glaviceps purpurea, the Ergot Fig. 387.—Various Ascomycetes. 1 Section through part of a Truffle (Tuber melanosporuw) showing a portion of the cortex (below) and a chamber containing oval asci, each of which contains 4 spores, 2 Vertical section of the apothecium of a discomycetous Lichen, Physcia eiliaris (after Sachs). * The Yeast-plant, Sacch/tromyces cerevisece. <, 5, 6 Single Yeast-cells showing development of a sprout, t A cell containing two spores. * x200; 2x60; Sx600; 1000. (Partly after Rees.) of Rye and other grasses, is a very interesting form. The spores attack the ovaries of Grasses and invest them with a mycelium from which conidia are abstricted in large numbers (fig. 386 ^). These can at once infect new plants. Gradually the whole ovary is replaced by a mass of fungal substance, the sclerotium. In the autumn at the time of harvest the ears of Rye may be seen with these dark sclerotia projecting from them (fig. 386 ^). Care has to be exercised that they do not get mixed up with the grain, as the Ergot contains an alkaloid and other poisonous substances, and if intermingled with food causes a disease which has received the name of ergotism. The sclerotia remain dormant through the winter,