Part 32

Scleroderma has a corky peridium. The fruit-bodies commence their development under ground. S. vulgare (Fig. 181 V-VII), has a hard, slaty-black gleba.

Order 4. =Nidulariaceæ= (=Nest-Fungi=). Small Fungi of which the fruit-body at first is spherical or cylindrical but upon maturity it becomes cupular or vase-like, and contains several lenticular “peridiola” lying like eggs in a nest. The peridiola are the chambers which contain the hymenium, covered by a thin layer of the gleba, all the remaining portion of the gleba becoming dissolved. On decaying wood.

Nidularia has spherical fruit-bodies containing a large number of lenticular peridiola, embedded in a slimy mass.--Crucibulum has fruit-bodies resembling crucibles with discoid peridiola, each with a spirally-twisted stalk.--Cyathus has a fruit-body, which when open is campanulate, with stratified peridium, and long-stalked, lense-shaped peridiola.

Order 5. =Hymenogastraceæ.= Fruit-bodies tubercular, globose and subterranean, resembling very closely the Truffles, from which they can only be distinguished with certainty by microscopic means. The peridium is simple, capillitium wanting, and the gleba encloses a system of labyrinthine passages covered with a continuous hymenium. The fruit-bodies persist for some time, and form a fleshy mass, the spores being only set free by the decay of the fruit-body, or when it is eaten by animals. The majority are South European. Hymenogaster, Melanogaster, Rhizopogon (Fig. 181 I-IV).

APPENDIX TO THE BASIDIOMYCETES:

Basidiolichenes (Lichen-forming Basidiomycetes).

Several Fungi belonging to the Basidiomycetes have a symbiotic relationship with Algæ exactly similar to that enjoyed by certain Ascomycetes, and these are therefore included under the term Lichens (p. 136). They are chiefly tropical.

Order 1. =Hymenolichenes.= To this order belong some gymnocarpic forms: Cora, Dictyonema, Laudatea.

Order 2. =Gasterolichenes.= To this belong some angiocarpic forms: Emericella, Trichocoma.

APPENDIX TO THE FUNGI.

Fungi imperfecti (Incompletely known Fungi).

1. The =Saccharomyces-forms= are Fungi which are only known in their yeast-conidial form. They are conidia of higher Fungi which can multiply to an unlimited extent by budding in nutritive solutions, and in this way maintain their definite size and shape. The budding takes place only at the ends of the conidia. The wall of the conidium forms at one or at both ends a small wart-like outgrowth, which gradually becomes larger, and is finally separated from its mother-cell as an independent cell, surrounded by a closed cell-wall (Fig. 182 a, b).

Under very favourable conditions multiplication occurs so rapidly that the daughter-cells themselves commence to form buds, before they have separated from their mother-cell, with the result that pearl-like chains of cells are produced. When the yeast-cells have only limited nutriment, with an abundant supply of air, at a suitable temperature, an endogenous formation of spores takes place. The protoplasm of the cells divides into 1–4 (rarely a greater number) masses (Fig. 182 c, d, e) which surround themselves with a thick cell-wall, and in this state can withstand adverse conditions and periods of dryness lasting for several months.

The sporangia are not asci since they have no definite form, and a definite number, form and size of spores is not found. The spores in the different species and kinds occupy varying periods for their development, although exposed to the same temperature, a fact of importance in determining one from another. On germination the wall of the mother-cell is destroyed, and each spore gives rise to a new cell, multiplication taking place by budding (Fig. 182 f). The majority of Yeast-Fungi are able to produce alcoholic fermentation in saccharine fluids.

The most important of these Fungi is the Beer-yeast (Saccharomyces cerevisiæ) with ovate, ellipsoidal or spherical cells (Fig. 182). It is a plant which has been cultivated from time immemorial, on account of its property of producing alcoholic fermentation in sugar-containing extracts (wort), derived from germinating barley (malt). Carbonic acid is also set free during this process. The “surface-yeast” (Fig. 182 a), which produces ordinary beer when the brewing takes place at higher temperatures, has cell-chains; “sedimentary yeast” (Fig. 182 b), used in the brewing of Bavarian beer, has spherical cells, solitary, or united in pairs. Both these and the following Yeast-Fungi include, according to Hansen, several species and kinds.

The “Ferment of Wine” (Saccharomyces ellipsoideus) produces wine in the juice of grapes. Uncultivated yeast-cells are always present on grapes; an addition of this species to the “must” is not necessary to secure fermentation. A large number of other “uncultivated” yeast-cells appear in breweries mixed with the cultivated ones, and cause different tastes to the beer (S. pastorianus, etc.). S. ludwigii, found, for instance, on the slimy discharge from Oaks, produces abundant cell-chains on cultivation. S. apiculatus is very frequently met with on all kinds of sweet fruits, it has orange-like cells. S. mycoderma has cylindrical cells, often united together in chains (Fig. 183): it forms a whitish-gray mass (“fleur de vin”) on wine, beer, fruit-juice, etc., standing in bottles uncorked or not entirely filled. It is thought that this Fungus causes decomposition and oxydises the fluid in which it is found, but it cannot produce alcoholic fermentation in saccharine liquids, and it does not form endospores; hence it is uncertain whether it is true Saccharomyces.

The “Dry-yeast” used in baking white bread is “surface-yeast.” In leaven, a kneaded mixture of meal, barm and water, which is used for the manufacture of black bread, Saccharomyces minor is present, and a species allied to this produces alcoholic fermentation in dough with the evolution of carbonic acid, which causes the dough to “rise.”

2. =Oidium-forms.= Of many Fungi only the Oidium-forms are known, which multiply in endless series without employing any higher form of reproduction. Oidium lactis (Fig. 184) is an imperfectly developed form which frequently appears on sour milk and cheese. It can produce a feeble alcoholic fermentation in saccharine liquids. Thrush or aphthæ (O. albicans) appears as white spots in the mouths of children. Several similar Oidium-forms are parasites on the skin and hair of human beings, and produce skin diseases, such as scurvy (O. schoenleinii) and ringworm (O. tonsurans).

3. =Mycorhiza.= These Fungi, which have been found on the roots of many trees and heath-plants, particularly Cupuliferæ and Ericaceæ, consist of septate hyphæ, and belong partly to the Hymenomycetes, partly to the Gasteromycetes. It has been shown that the Mycorhiza enters into a symbiotic relationship with the roots of higher plants.

DIVISION II.

MUSCINEÆ (MOSSES).

In this Division a well-marked alternation of generations is to be found. The development of the first or sexual generation (gametophyte), which bears the sexual organs, antheridia and archegonia, commences with the germination of the spore, and consists, in the Liverworts, of a thallus, but in the true Mosses of a filamentous protonema, from which the Moss-plant arises as a lateral bud. The second or asexual generation (sporophyte), developed from the fertilised oosphere, consists of a sporangium and stalk.

=The sexual generation, the gametophyte.= The protonema in the Liverworts is very insignificant, and not always very sharply demarcated from the more highly developed parts of the nutritive system. In the true Mosses the protonema is well-developed, and consists of a branched, alga-like filament of cells, the dividing cell-walls being always placed obliquely. In the parts exposed to the light it is green, but colourless or brownish in those parts which are underground (Fig. 186). The protonema is considered to be a lower form of the stem, and grows in the same manner by means of an apical cell; at its apex it may directly develope into a leaf-bearing stem, or these arise from it as lateral branches (Fig. 186 k).

The more highly differentiated part of the vegetative system, the “Moss-plant,” which is thus developed from the protonema, is in the “thalloid” Liverworts generally a dichotomously-branched thallus without any trace of leaf-structures (Fig. 194); in Marchantia (Fig. 197) and others, scale-like leaves (amphigastria) are found on the under surface. The higher Liverworts and the Leafy-Mosses are differentiated into a filamentous, ramified stem with distinct leaves arranged in a definite manner, resembling the stem and leaves of the higher plants (Figs. 186, 195, 200).

True roots are wanting, but are biologically replaced by rhizoids. These are developed on the stems or thallus: in the Liverworts they are unicellular, but in the Leafy-Mosses generally multicellular and branched. In the latter group they are considered identical with the protonema, and may become true protonema, and new plants may be developed from them (Fig. 186 b).

The internal structure of the sexual generation is very simple. The leaves in nearly all cases are formed of a single-layered plate of cells; in the Leafy-Mosses, however, a midrib is very often formed, and sometimes, also, marginal veins; and along these lines the leaves are several layers of cells in thickness. The stem is constructed of cells longitudinally elongated, the external ones of which are narrower and sometimes have thicker walls than the more central ones. Vessels are not found, but in several Mosses there is in the centre of the stem a conducting strand of narrow, longitudinal cells, which represents the vascular bundle in its first stage of development. This strand contains elements for conveying water as well as sieve-tubes. Stomata are entirely wanting in the sexual generation of the Leafy-Mosses; they are found in a few Liverworts (Marchantia), but their structure is not the same as in the higher plants.

VEGETATIVE REPRODUCTION takes place by gemmæ or buds which arise on the protenema, the rhizoids, the thallus, or the shoots, and become detached from the mother-plant; or else the protonema and the older parts of the plant simply die off, and their branches thus become independent plants. This well-developed vegetative reproduction explains why so many Mosses grow gregariously. In certain Marchantiaceæ special cupules, in which gemmæ are developed, are found on the surface of the thallus (Fig. 197 A, s-s). Again, protonema may also arise from the leaves, and thus the leaves may act as reproductive bodies. Certain Mosses nearly always reproduce vegetatively, and in these species the oospheres are seldom fertilised.

The first generation bears the SEXUAL ORGANS; both kinds are found either on the same plant (monœcious), or on separate plants (diœcious). In the thalloid Liverworts they are often situated on the apex of small stems (gametophores), springing from the surface of the thallus. In the Leafy-Liverworts and true Mosses the leaves which enclose the sexual organs often assume a peculiar shape, and are arranged more closely than the other leaves to form the so-called “Moss-flower.” The male sexual organs are called antheridia. They are stalked, spheroid, club- or egg-shaped bodies whose walls are formed of one layer of cells (Fig. 187), enclosing a mass of minute cubical cells, each one of which is a mother-cell of a spermatozoid. The spermatozoids are self-motile; they are slightly twisted, with two cilia placed anteriorly (Fig. 188), while posteriorly they are generally a trifle club-shaped, and often bear at that part the remains of the cytoplasm, the spermatozoid itself being formed from the nucleus. In the presence of water the ripe antheridium bursts, and its contents are ejected; the spermatozoids, being liberated from their mother-cells, swarm about in the water in order to effect fertilisation.