Page:EB1911 - Volume 16.djvu/601

Rh are able to develop with or without fusion. The most satisfactory view in the present state of our knowledge seems to be that the spermatia are male cells which, while retaining their fertilizing action in a few cases are now mainly functionless. The female sexual organs, the ascogonia, would thus in the majority of cases develop by the aid of some reduced sexual process or the ascocarps be developed without relation to sexual organs. A further argument in support of this view is that it is in complete agreement with what we know of the sexuality of the ordinary, free-living ascomycetes, where we find both normal and reduced forms (see ).

Fruit Bodies.—We find two chief types of fruit bodies in the lichens, the perithecium and apothecium; the first when the fungal element is a member of the Pyrenomycetes division of the Ascomycetes, the second when the fungus belongs to the Discomycetes division. In the two genera of lichens—the Basidiolichens—in which the fungus is a member of the Basidiomycetes, we have the fructification characteristic of that class of fungi: these are dealt with separately. The perithecium is very constant in form and since the gonidia take no part in the formation of this organ or that of the apothecium it has the general structure characteristic of that division of fungi. The apothecia, though of the normal fungal type and usually disk-shaped, are somewhat more variable, and since the variations are of value in classification some more details may be added.

They present various shapes, of which the following are the principal: (a) peltate, which are large, rounded, without any distinct thalline margin (e.g. Usnea, Peltigera); (b) lecanorine, or scutelliform, which are orbicular and surrounded by a distinct, more or less prominent thalline margin (e.g. Parmelia, Lecanora), having sometimes also in addition a proper one (e.g. Thelotrema, Urceolaria); (c) lecideine, or patelliform, which are typically orbicular, with only a proper margin (e.g. Lecidea), sometimes obsolete, and which are occasionally irregular in shape, angular or flexuose (e.g. Lecidea jurana, L. myrmecina), or complicated and gyrose (e.g. Gyrophora), and even stipitate (e.g. Baeomyces); (d) lirelliform, which are of very irregular figure, elongated, branched or flexuose, with only a proper margin (e.g. Xylographa, Graphis, &c.) or none (e.g. some Arthoniae), and often very variable even in the same species. In colour the apothecia are extremely variable, and it is but rarely that they are the same colour as the thallus (e.g. Usnea, Ramalina). Usually they are of a different colour, and may be black, brown, yellowish, or also less frequently rose-coloured, rusty-red, orange-reddish, saffron, or of various intermediate shades. Occasionally in the same species their colour is very variable (e.g. Lecanora metaboloides, Lecidea decolorans), while sometimes they are white or glaucous, rarely greenish, pruinose. Lecideine apothecia, which are not black, but otherwise variously coloured, are termed biatorine.

The two principal parts of which an apothecium consists are the hypothecium and the hymenium, or thecium. The hypothecium is the basal part of the apothecium on which the hymenium is borne; the latter consists of asci (thecae) with ascospores, and paraphyses. The paraphyses (which may be absent entirely in the Pyrenolichens) are erect, colourless filaments which are usually dilated and coloured at the apex; the apices are usually cemented together into a definite layer, the epithecium (fig. 14). The spores themselves may be unicellular without a septum or multicellular with one or more septa. Sometimes the two cavities are restricted to the two ends of the spore, the polari-bilocular type and the two loculi may be united