Fungi: Their Nature and Uses

by M. C. Cooke

The epispore acquires a waxy consistence by this pigmentation, so that it may be detached in granules. It is to this particular consistency of the epispore that the cracks so frequent in the coloured sporidia of Ascobolus are due, through contraction of the epispore. As they approach maturity, the sporidia accumulate towards the apex of the asci, and finally escape in the manner already indicated.

In all essential particulars there is a great similarity in the structure of the other Discomycetes, especially in their reproductive system. In most of them coloured sporidia are rare. In some the receptacle is pileate, clavate, or inflated, whilst in Stictis it is very much reduced, and in the lowest form of all, Ascomyces, it is entirely absent. In the Phacidiacei, the structure is very similar to that of the Elvellacei, whilst the Hysteriacei, with greater affinities with the latter, still tend towards the Pyrenomycetes by the more horny nature of the receptacle, and the greater tendency of the hymenium to remain closed, at least when dry. In some species of Hysterium, the sporidia are remarkably fine. M. Duby[AA] has subjected this group to examination, and M. Tulasne partly so.[AB]

Sphæriacei.—In this group there is considerable variation, within certain limits. It contains an immense number of species, and these are daily being augmented. The general feature in all is the presence of a perithecium, which contains and encloses the hymenium, and at length opening by a pore or ostiolum at the apex. In some the perithecia are simple, in others compound; in some immersed in a stroma, in others free; in some fleshy or waxy, in others carbonaceous, and in others membranaceous. But in all there is this important difference from the Ascomycetes we have already had under consideration, that the hymenium is never exposed. The perithecium consists usually of an external layer of cellular structure, which is either smooth or hairy, usually blackish, and an internal stratum of less compact cells, which give rise to the hymenium.

Fig. 35.—Perithecium of Sphæria and Section.

As in the Discomycetes, the hymenium consists of asci, paraphyses, and mucilage, but the whole forms a less compact and more gelatinous mass within the perithecium. The formation and growth of the asci and sporidia differ little from what we have described, and when mature the asci dehisce, and the sporidia alone are ejected from the ostiolum. We are not aware that operculate asci have yet been detected. It has been shown in some instances, and suspected in others, that certain moulds, formerly classed with Mucedines and Dematiei, especially in the genus Helminthosporium, bear the conidia of species of Sphæria, so that this may be regarded as one form of fruit.

Perithecia, very similar externally to those of Sphæria, but containing spores borne on slender pedicels and not enclosed in asci, have had their relations to certain species of Sphæria indicated, and these are no longer regarded so much as species of Hendersonia or Diplodia as the pycnidia of Sphæria. Other and more minute perithecia, containing minute, slender stylospores in great numbers, formerly classed with Aposphæria, Phoma, &c., but are now recognized as spermogonia containing the spermatia of Sphæriæ. How these influence each other, when and under what circumstances the spermatia are instrumental in impregnation of the sporidia, is still matter of mystery. It is clear, however, that in all these conidia, macrospores, microspores, and some spermatia, or by whatever names they may be called, there exists a power of germination. Tulasne has indicated in some instances five or six forms of fruit as belonging to one fungus, of which the highest and most perfect condition is a species of Sphæria.

Fig. 36.—Uncinula adunca.

Perisporiacei.—Except in the perithecia rupturing irregularly, and not dehiscing by a pore, some of the genera in this group differ little in structure from the Sphæriacei. On the other hand, the Erysiphei present important and very interesting features. They occur chiefly on the green parts of growing plants. At first there is a more or less profuse white mycelium.[AC] This gives rise to chains of conidia (Oidium), and afterwards small sphæroid projections appear at certain points on the mycelium. These enlarge, take an orange colour, ultimately passing into brown, and then nearly black. Externally these perithecia are usually furnished with long, spreading, intertwined, or branching appendages, sometimes beautifully branched or hooked at their tips. In the interior of the receptacles, pear-shaped or ovate asci are formed in clusters, attached together at the base, and containing two or more hyaline sporidia. Other forms of fruit have also been observed on the same mycelium. In an exotic genus, Meliola, the fulcra, or appendages, as well as the mycelium, are black, otherwise it is very analogous to such a genus of Erysiphei as Microsphæria. In Chætomium, the perithecia bristle with rigid, dark-coloured hairs, and the sporidia are coloured. Our limits, however, will not permit of further elucidation of the complex and varied structure to be found amongst fungi.[AD]