Chapter VIII: 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_),[16] 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.

The female sexual organs are termed _archegonia_. They are flask-shaped bodies (Fig. 189), the lower, swollen portion (_venter_) having a wall, in most cases from 1–2 cells thick, enclosing the oosphere (Fig. 189 _B_, _k_): the long neck is formed of tiers of 4–6 cells, enclosing a central row of cells--_the neck-canal-cells_ (Fig. 189 _A_). When the archegonium is fully developed, the walls of the neck-canal-cells become mucilaginous and force open the neck of the archegonium. The mucilage thus escapes, and, remaining at the mouth of the archegonium, acts in a somewhat similar manner to the stigma and conducting tissue of a carpel, by catching and conducting the spermatozoids to the oosphere (Fig. 189 _B_, _m_), with whose cell-nucleus they coalesce. With regard to the formation of the oosphere, it may further be remarked that the lower part of the archegonium originally encloses the so-called “central cell”; but shortly before the archegonium is ripe, this cuts off a small portion, _the ventral-canal-cell_, which lies immediately beneath the neck, and the larger, lower portion becomes the oosphere.

The organs mentioned here, antheridia and archegonia, are
present in the Cryptogams (Pteridophyta) and the Gymnosperms.
They have always the same fundamental structure, but with slight
modifications of detail. These plants are therefore known as the
ARCHEGONIATA.

The fertilisation of the Mosses cannot be effected without water. Rain and dew therefore play a very important part in this process, and for this end various modifications of structure are found.

Among the sexual organs, paraphyses--filamentous or club-shaped bodies--are to be found.

=The asexual generation, the sporophyte= (Moss-fruit or sporogonium). As the result of fertilisation the oosphere surrounds itself with a cell-wall, and then commences to divide in accordance with definite laws.[17] The embryo (Fig. 189 _C_) produced by these divisions remains inside the wall _a-a_ of the archegonium (Figs. 190, 199 _D_, _E_), and developes into the _sporogonium_, which remains attached to the mother-plant, often nourished by it, as if the two were one organism. The lower extremity of the sporogonium, _the foot_ (Figs. 190 _f_; 199 _D_), very often forces its way deep down into the tissue of the mother-plant, but without an actual union taking place. The central portion of the sporogonium becomes a shorter or longer _stalk_ (_seta_), while the sporangium itself is developed at the summit. At a later stage, during the formation of the spores, the sporangium very often assumes the form of a _capsule_, and dehisces in several ways characteristic of the various genera (Figs. 192, 193, 194, 195, 200). The basal portion of the archegonium grows for a longer or shorter period, forming a sheath, the _calyptra_, in which the capsule is developed, but eventually it ceases to enlarge, and is then ruptured in different ways, but quite characteristically, in each group. Anatomically, the asexual generation is often more highly differentiated than the sexual; thus, for instance, stomata are present on the sporangia of the true Mosses, but are absent in the sexual generation.

As the capsule developes, an external layer of cells--the _amphithecium_--and an internal mass--the _endothecium_--are differentiated. As a rule the former becomes the wall of the capsule while the latter gives rise to the spores. In this Division, as in the Pteridophyta, the name _archesporium_ (Fig. 190 _t_) is given to the group of cells inside the sporangium which gives rise to the mother-cells of the spores. The archesporium is in general a unicellular layer; in _Sphagnum_ and _Anthoceros_ it is derived from the most internal layer of the amphithecium, but with these exceptions it arises from the endothecium, usually from its most external layer. In the true Mosses and in _Riccia_ only spore-mother-cells are produced from the archesporium, but in the majority of the Liverworts some of these cells are sterile and become elaters (cells with spirally thickened walls, Figs. 196, 189), or serve as “nurse-cells” for the spore-mother-cells, which gradually absorb the nutriment which has been accumulated in them. In _Anthoceros_, and almost all the Leafy-Mosses, a certain mass of cells in the centre of the sporangium (derived from the endothecium) does not take part in the formation of the archesporium, but forms the so called “column” or “columella” (Figs. 190, 191).

The _spores_ arise in _tetrads_, _i.e._ four in each mother-cell, and are arranged at the corners of a tetrahedron, each tetrahedron assuming the form of a sphere or a triangular pyramid. The mature spore is a nucleated mass of protoplasm, with starch or oil as reserve material. The wall is divided into two layers: the external coat (exospore) which is cuticularized and in most cases coloured (brown, yellowish), and the internal coat (endospore), which is colourless and not cuticularized. On germination the exospore is thrown off, the endospore protrudes, and cell-division commences and continues with the growth of the protonema (Fig. 186, _B-D_).

The morphological explanation which Celakovsky has given of
the sporogonium, and which is not at all improbable, is, that
it is homologous with an embryo consisting of a very small
stem-portion and a terminal spore-producing leaf. This will be
further explained in the introduction to the Flowering-plants
(p. 236).

In the Liverworts the young sporogonium lives like a parasite, being nourished by the sexual generation (only in _Anthoceros_ has it a slight power of assimilation). In the Leafy-Mosses, on the other hand, with regard to the power of assimilation, all transitions are found from abundant assimilation (_Funaria_, _Physcomitrium_) to almost complete “parasitism” (_Sphagnum_, _Andreæa_). In the majority of the operculate Mosses the sporogonium has a more or less perfect system of assimilation, and is able itself to form a large portion of the material necessary for the development of the spores, so that it chiefly receives from the sexual generation the inorganic substances which must be obtained from the soil. The more highly developed the assimilative system of the sporogonium, the more stomata are present.

APOSPORY. In some operculate Mosses it has been possible to
obtain a protonema with small Moss-plants from the seta, when
severed from its Moss-plant, and grown on damp sand.

The Mosses are the lowest plants which are provided with stem and leaf. They are assigned a lower place when compared with the higher Cryptogams, partly because there are still found within the Division so many forms with a mere thallus, partly because typical roots are wanting and the anatomical structure is so extremely simple, and partly also because of the relation between the two generations. The highest Mosses terminate the Division, the Muscineæ and Pteridophyta having had a common origin in the Algæ-like Thallophyta.

They are divided into two classes:--

HEPATICÆ, or Liverworts.

MUSCI FRONDOSI. True Mosses or Leafy-Mosses.

Class 1. =Hepaticæ= (=Liverworts=).

The protonema is only slightly developed. The remaining part of the vegetative body is either a prostrate, often dichotomously-branched thallus, pressed to the substratum (thalloid Liverworts), with or without scales on the under side (Figs. 194, 197); or a thin, prostrate, creeping stem, with distinctly-developed leaves, which are borne in two or three rows (Figs. 195, 198), viz., two on the upper and, in most cases, one on the under side. The leaves situated on the ventral side (amphigastria) are differently shaped from the others (Fig. 198 _a_), and are sometimes entirely absent. In contradistinction to the Leafy-Mosses, stress must be laid on the _well-marked dorsiventrality_ of the vegetative organs; _i.e._ the very distinct contrast between the dorsal side exposed to the light and the ventral side turned to the ground. Veins are never found in the leaves.

The _ventral part of the archegonium_ (calyptra) continues to grow for some time, and encloses the growing embryo, but when the spores are ripe it is finally ruptured by the sporangium, and remains situated like a sheath (_vaginula_) around its base. The sporangium opens, longitudinally, by _valves_ or _teeth_ (Fig. 194, 195, 197 _b_), very rarely by a lid, or sometimes not at all. _A columella is wanting_ (except in _Anthoceros_, Fig. 194); but on the other hand, a few of the cells lying between the spores are developed into _elaters_ (Fig. 196), _i.e._ spindle-shaped cells with spirally-twisted thickenings, which are hygroscopic, and thus serve to distribute the spores. (They are seen in Fig. 189 _C_, not yet fully developed, as long cells radiating from the base of the sporangium. They are wanting in _Riccia_).

Round the entire archegonium, (or group of archegonia, when
several are developed on the same receptacle) a sheath--the
_involucre_--is often formed, which persists, and encloses the
base of the stalk of the sporangium, together with the sheath
of the archegonium (Fig. 195 _p_). In the Marchantiaceæ each
archegonium is enclosed in a loose investment, the perigynium,
which is developed as an outgrowth from the cells of its stalk.

The majority of the Liverworts are found in damp and shady places, pressed to the substratum; a few are found floating in fresh water.

Family 1. =Marchantieæ.=

This embraces only forms with a thallus, which is more or less distinctly dichotomously branched, in some, one or two rows of thin leaves are situated on its under surface. On the upper surface of the thallus are found large air-chambers.

Order 1. =Ricciaceæ.= The sporogonia are, with the exception of a few genera, situated singly on the surface of the thallus, and consist only of a capsule without foot or stalk. They always remain enclosed by the wall of the archegonium (calyptra), and open only by its dissolution. Elaters are not developed. Some genera are found floating like Duckweed.--_Riccia glauca_ grows on damp clay soil. _R. fluitans_ and _R. natans_ float in stagnant waters.

Order 2. =Corsiniaceæ.= (Not native). Intermediate forms between the preceding and the following order. In internal and external structure mainly resembling the Marchantiaceæ. _Corsinia_; _Boschia_.

Order 3. =Marchantiaceæ=, are large, fleshy forms. The surface of the thallus is divided into small rhombic areas, in the centre of each of which is found a large, peculiarly constructed stoma (Fig. 197 _A_); beneath each of these a large air-cavity is to be found. From the floor of the air-cavity a number of alga-like cells project into it; these contain chlorophyll and are therefore the assimilating cells. The antheridia and archegonia are each found aggregated on specially formed branches (somewhat resembling Mushrooms) projecting from the surface of the thallus. The antheridia are developed on the upper surface (Fig. 197 _C_, _D_) and the archegonia on the lower (Fig. 197 _A_, _B_), near the centrally-placed stalk.

_Marchantia polymorpha_ is diœcious (Fig. 197), and very common on damp places. _Lunularia_ (South Europe), frequently found on flower-pots in conservatories; _Preissia_, _Fegatella_, _Reboulia_, _Targionia_.

Family 2. =Anthoceroteæ.=

These have an entirely leafless, fleshy, flat, and
irregularly-shaped thallus. In its intercellular chambers
Nostoc-colonies are often found, which have forced their way
through the stomata situated on the under side. The antheridia
and archegonia arise from the cells lying inside the thallus.
The capsule resembles a long, thin pod; it has two valves and a
columella. _Anthoceros_ (_A. lævis_, Fig. 194, and _punctatus_).

Family 3. =Jungermannieæ.=

Some forms in this family have a thallus in which leaf-like structures are found (_Blasia_), while in others (_e.g. Metzgeria_, _Pellia_, _Aneura_) they are entirely absent. The majority, however, have round, thick stems, bearing dorsally two rows of leaves, and one row ventrally. Some of these have the leaves “underlying” (Fig. 195), while in others (Fig. 198) they are “overlying.” (See Figs. 195, 198, with explanation).

The sporangia are spherical, stalked, and situated singly on the apex of the branches, and open by four valves (in _Sphærocarpus_ they are indehiscent).

All the species in this family were formerly reckoned as belonging to one genus, _Jungermannia_, but now they are divided into several, arranged as follows:--