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 Fungi).
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From Beiträge zur Wissenschaftlichen Botanik. |
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Fig. 9.—Section of Heteromerous Lichen Thallus. |
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a, Upper cortical layer. d, Lower cortical layer. c, Medullary layer. b, Gonidial layer. |
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.
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After Bornet, from De Bary’s Vergleichende Morphologie und Biologie der Pilze, Myceiozoen und Bacterien, by permission of Wilhelm Engelmann. |
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Fig. 11.—Lichen-forming Algae. (A, C, D, E mag. 950, B 650 times.) The alga is in all cases indicated by the letter g, the assailing hyphae by h. A, Pleurococcus, Ag. (Cystococcus, Näg.) attacked by the germ-tube from a spore of Physica parietina. B, Scytonema from the thallus of Stereocaulon famulosum. C, Nostoc from the thallus of Physma chalazanum. D, Gloeocapsa from the thallus of Synalissa Symphorea. E, Pleurococcus Sp. (Cystococcus) from the thallus of Cladonia furcata. |
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After Schwendener, from De Bary’s Vergleichende Morphologie und Biologie der Pilze Mycetozoen und Bacterien, by permission of Wilhelm Engelmann. |
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Fig. 12.—Usnea barbata. (Mag. more than 500 times.) |
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c, An isolated mature soredium, with an algal cell (Pleurococcus) in the envelope or hyphae. d, Another with several algal cells in optical longitudinal section. e, f, Two soredia in the act of germinating; the hyphal envelope has grown out below into rhizoid branches, and above shows already the structure of the apex of the thallus (see fig. 9). |
They present various shapes, of which the following are the principal: (a) peltate, which are large, rounded, without any distinct thalline margin[1] (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[1] (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.
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After Tulasne, from De Bary’s Vergleichende Morphologie und Biologie der Pilze, Mycetozoen und Bacterien, by permission of Wilhelm Engelmann. |
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Fig. 13.—A, B, Gyrophora cylindrica. (A mag. 90, B 390 times, C highly magnified.) |
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A, A vertical median section through a spermogonium imbedded in the thallus. o, Upper rind. u, Under rind. m, Medullary layer of the thallus. B, Portion of a very thin section from the base of the spermogonium. w, Its wall from which proceed sterigmata with rod-like spermatia (s). m, Medullary hyphae of the thallus. C, Cladonia novae Angliae, Delise; sterigmata with spermatia from the spermogonium. |
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
