Chapter VI: Mosses, or Mus´ci (muscus, Moss)

I need scarcely refer to the figures in Pl. III. to enable the reader to recognize the Mosses; every one knows them at once by their remarkably uniform general appearance, their miniature-plantlike form, their crowded little leaves, concealing the slender wiry stems, their growth in patches, and their curious urn-shaped fruits raised up on slender bristle-like stalks.

The leaves of the mosses are simple, _i. e._ not cut into segments, and consist of one or two layers of cells. The thinness of the leaves enables these cells to be seen very distinctly, the closely united cell-walls giving the leaves a netted or reticulated appearance (fig. 48), and the grains of chlorophyll being generally few and readily distinguished. The veins of the leaves, or the nerves as they are usually called, scarcely deserve the name; for neither they nor even the stems contain fibro-vascular tissue, but consist simply of elongate closely packed cells, and often the leaves have no nerves.

The fruit of the mosses consists of a _capsule_, sometimes called a _sporan´gium_ (σπορἀ, seed, ἄγγος, vessel), usually placed at the end of a slender stalk, called the _séta_ (_seta_, a bristle); but sometimes the stalk is absent or extremely short, when the capsule is said to be ses´sile (_sessilis_, sitting). The young capsule is covered with a thin extinguisher-like cap or _calyp´tra_ (καλὑπτρα, a cover), which is carried up as the capsule and its stalk grow, so as to be either entirely thrown off, or to remain covering a greater or less portion of the capsule, when this attains maturity.

PLATE III. [PAGE 54.]

MOSSES.

Fig.

1. _Sphagnum acutifolium_, expanded leaf.

2. _Sphagnum acutifolium_, cells of leaf.

3. Spermatozoa of _Polytrichum piliferum_.

4. _Sphagnum acutifolium._

5. _Sphagnum acutifolium_, capsule.

6. _Gymnostomum truncatulum._

7. _Gymnostomum truncatulum_, leaf.

8. _Gymnostomum truncatulum_, capsule and operculum.

9. _Gymnostomum truncatulum_, spore.

10. _Dicranum heteromallum._

11. _Dicranum heteromallum._

12. _Dicranum heteromallum_, leaf.

13. _Dicranum heteromallum_, operculum.

14. _Dicranum heteromallum_, calyptra.

15. _Dicranum heteromallum_, capsule; 15 _a_, peristome.

16. _Tortula muralis._

17. _Tortula muralis_, leaf.

18. _Tortula muralis_, capsule; _a_, tooth of peristome.

19. _Tortula muralis_, operculum.

20. _Tortula muralis_, calyptra.

21. _Tortula muralis_, archegonia.

22. _Polytrichum piliferum._

23. _Polytrichum piliferum_, leaf.

24. _Polytrichum piliferum_, calyptra.

25. _Polytrichum piliferum_, antheridial stems.

26. _Polytrichum piliferum_, single head.

27. _Polytrichum piliferum_, antheridia and paraphyses.

28. _Funaria hygrometrica._

29. _Funaria hygrometrica._

30. _Funaria hygrometrica_, leaf.

31. _Funaria hygrometrica_, capsule; _a_, operculum.

32. _Funaria hygrometrica_, stalk-like body.

33. _Funaria hygrometrica_, young archegone.

34. _Funaria hygrometrica_, more advanced archegone.

35. _Funaria hygrometrica_, section of young capsule.

36. _Funaria hygrometrica_, calyptra.

37. _Funaria hygrometrica_, antheridia.

38. _Funaria hygrometrica_, spores.

39. _Funaria hygrometrica_, annulus.

40. _Funaria hygrometrica_, archegonia.

41. _Funaria hygrometrica_, antheridial head.

42. _Funaria hygrometrica_, peristome.

43. _Hypnum rutabulum._

44. _Hypnum rutabulum_, leaf.

45. _Hypnum rutabulum_, capsule.

46. _Hypnum rutabulum_, spores.

47. _Hypnum rutabulum_, peristome.

48. _Hypnum rutabulum_, cells of leaf.

49. _Bryum capillare._

W Bagg sculp

_London: John Van Voorst._]

The calyptra is either simply mitre-shaped, or _mítriform_ (Pl. III. fig. 24), or it is half-cleft, or _dimid´iate_ (figs. 14, 36). When the capsule is ripe, the upper part usually separates at a circular horizontal line (fig. 8) as a kind of lid, which is called the _oper´culum_ (_operculum_, a lid), and thus the spores are enabled to escape. The rim of the capsule, from which the operculum has separated, forms its mouth, and this often exhibits a fringe of teeth (figs. 15, 18, 31), arranged in one or more rows; sometimes the teeth are replaced by a membrane, or, again, both teeth and a membrane may be present. This mouth-fringe is the _per´istome_ (περἰ, around, στὁμα, mouth). In many mosses, an elastic row or ring of cells is situated between the mouth of the capsule and its operculum, called the _annulus_ (figs. 18 & 39); this, when the capsule is ripe, aids in throwing off the operculum.

It is important to become acquainted with the structure and arrangement of these parts, as they form characters by which the families and genera of mosses are distinguished.

The capsules of the mosses form very beautiful microscopic objects, especially those furnished with a toothed peristome.

Most of the mosses produce their fructification in the winter and spring.

The class of mosses is divided into two Orders, according to whether the fruit-stalk is terminal, _i. e._ arises from the end of the stem or its branches, or whether it is lateral, arising from the side of the stem. Those with the fruit-stalk terminal, or the end fruited (Pl. III. fig. 22), form the _Ac´rocarpi_ (ἄκρα, summit, καρπὀς, fruit); while those with the fruit-stalks lateral, or the side-fruited mosses (fig. 43), constitute the _Pleu´rocarpi_ (πλευρἀ, side). The new shoots or young branches of the stems of mosses are termed _innovations_.

We will now examine a few common mosses more in detail, beginning with the ACROCARPI.

_Sphag´num acutifólium_ (Pl. III. fig. 4) is found in pools or bogs, growing at the margins so as to be partially immersed. In this moss, the upper branches are grouped into a head. The leaves are crowded, and overlapping or im´bricate (_imbrex_, a tile) on the elongate stems; they are egg-shaped (ovate) on the main stems (fig. 1), and narrower or ovate-lanceolate on the branches; they are nerveless, and finely toothed at the apex. The capsule (fig. 5) is roundish-ovate, without a peristome, and the operculum is flattened. The grouped arrangement of the upper branches renders the species of _Sphagnum_ easily recognized. The structure of the leaves is also very peculiar and characteristic (fig. 2). The cells of which they consist are of two kinds, one (fig. 2 _a_) being colourless, elongate, pointed, and containing a spiral fibre; the other consisting of shorter and narrower obtuse cells, containing chlorophyll, and situated between the former. In many of the former kind of cells, little round apertures exist on the under surface, and minute animals may sometimes be found imprisoned in them.

Another species of _Sphagnum_, _S. obtusifolium_, is common, and greatly resembles the above, but has shorter and thicker stems, and rounded-ovate, very concave, and obtuse leaves.

_Gymnos´tomum truncat´ulum_ (Pl. III. fig. 6) is a common little moss, found on banks and in fields and gardens.

In this there is no peristome, although, in the young condition, a membrane extends more or less over the interior of the mouth of the capsule. The stem is slender, rigid, and simple, or but little branched. The calyptra is dimidiate; the operculum is present (fig. 8), and terminates above in an oblique beak, or it is obliquely rostrate (_ros´trum_, a beak) as it is called. The leaves are obovate (fig. 7) or ovate with the broader part remote from the stem, and narrowed at the apex, where the nerve protrudes or is ex´current (_excurro_, to run out). The spores (fig. 9) are reddish brown and smooth.

_Dicránum heteromal´lum_ (Pl. III. figs. 10 & 11) is probably the first moss the reader will meet with on banks and heaths in the early spring; and it will be sure to be noticed on account of the bright green colour of the patches and the beautiful orange-brown capsules.

In this moss the capsule is nodding (cer´nuous) (Pl. III. fig. 15), and has a single peristome, consisting of sixteen equidistant teeth, each being deeply cut or cleft longitudinally (fig. 15 _a_), so that there are thirty-two teeth altogether; and these are marked with internal cross-bars, or transverse ridges. The calyptra is dimidiate (fig. 14); and the lid is furnished with a long oblique beak (fig. 15 _b_). The leaves are crowded, strongly nerved (fig. 12), lanceolate at the base, and very narrow towards the apex, which is toothed; they are, moreover, curved, and bent towards one side, or sécund.

_Tor´tula murális_ (Pl. III. fig. 16) may be found on the top of almost every wall and on waste ground.

In this moss the peristome is single (fig. 18), consisting of thirty-two spirally twisted teeth, arranged in pairs. They are narrow and slender, and each is composed of two longitudinal portions (fig. 18 _a_), one of which is pale yellow, the other reddish brown, like the capsule, and both are fringed and covered with very minute papillæ. The capsule (fig. 18) is oblong, the ring or annulus remaining for some time. The lid is conical (fig. 19), with a longish somewhat oblique beak, and the calyptra is dimidiate (fig. 20). The stems are very short; the leaves (fig. 17) are oblong, obtuse; the nerve strong, and projecting as a colourless spirally striated bristle. The bristles often give the patches of the moss a hoary appearance on wall-tops. The margins of the leaves are folded back or recurved, giving them a peculiar thickened appearance.

The largest of our mosses are contained in the next genus, viz. _Polyt´richum_, some of them having the stems from 2 to 4 inches, or even more, in height; they are common on heaths and in woods.

_Polyt´richum pilif´erum_ (Pl. III. fig. 22) is very common on open dry heaths. This moss has simple stems, with the leaves crowded on the lower part of those which are fertile or fruit-bearing. The fruit-stalk is terminal (acrocarpous); the capsule ovate, 4-sided or quadrangular, with a knob or struma (_strúma_, a swelling) at the base, the lid having a short beak. The calyptra (fig. 24) is half-cleft (dimidiate) and very hairy. The peristome is single, and consists of sixty-four teeth. The leaves (fig. 23) are lanceolate, nearly upright, the margins folded inwards or inflexed; and they end abruptly in a saw-edged or serrated hair-like point.

_Poly´trichum commúne_, which is also very common, is larger than the last species, and may easily be distinguished by the curved and serrate leaves, which have no bristle-point.

In the early spring, patches of both these mosses may be found, in which the stems are terminated by little rosettes (figs. 25 & 26); these will be referred to presently.

Keeping still to the end-fruited or Acrocarpous mosses, we have next to mention _Funa´ria hygromet´rica_ (Pl. III. figs. 28, 29), which is readily distinguished from most other mosses by the pale apple-green colour which it possesses before the capsule ripens. It is extremely common on walls and waste ground.

The capsule of this moss (fig. 31) differs from those of the preceding mosses in the peristome being double (fig. 42), or composed of an outer and an inner row of teeth. The outer row consists of sixteen oblique reddish teeth, which are marked with transverse bars or trabe´culæ (_trabecula_, a little beam), and their points are connected by a net-like thin plate. The inner row contains also sixteen teeth, arising from the division of the membrane lining the capsule; these are yellowish, thin, and placed opposite the outer teeth. The capsule itself is pear-shaped or pyriform, orange-red when ripe, curved, and with the mouth oblique. The calyptra (fig. 36) is half-cleft, and expanded as if blown out below. The lid (fig. 31 _a_) is convex and obtuse; and the annulus (fig. 39) is large and easily separable. The fruit-stalks are curved near the top. The leaves (fig. 30) are ovate, concave, entire, with a nerve reaching the apex, which is acute and prolonged into a little point, or apic´ulate. The spores (fig. 38) are small and reddish brown. The specific name (_hygromet´rica_) of this moss expresses its hygrometric property; for if either the recent and moist moss be dried or the dry moss wetted, the fruit-stalk gradually twists in opposite directions in the two cases.

The last of the Acrocarpous mosses which we shall notice, _Bry´um capil´lare_ (Pl. III. fig. 49), is tolerably common on trunks of trees, on the ground, and sometimes on walls.

The capsule of this moss has a double peristome or mouth-fringe; the outer consisting of sixteen reddish-brown, equidistant, transversely striped teeth; the inner composed of sixteen thin keeled teeth, more or less split down the middle, and with two or three intermediate cilia. The capsule is nodding, smooth, oblong, pear-shaped, slightly narrowed below the mouth; the lid being somewhat convex, and furnished with a short slender beak. The calyptra is dimidiate. The leaves (fig. 50) are obovate, the nerve extending beyond the point, rendering them bristle-pointed. The seeds (fig. 49 _a_) are small and green.

This moss serves to illustrate a great difficulty, which will often occur to the student, in determining whether a moss is end-fruited or side-fruited. For in this, as in many other end-fruited mosses, a little side-shoot or young branch (innovation) grows from the main stem immediately below the leaves surrounding the base of the fruit-stalk, so that the fruit-stalk appears to arise from the side of the stem. The only method of overcoming the difficulty is to examine carefully the comparative size and thickness of the stem and the shoot, and to determine which is the weaker and so the newer. The leaves surrounding the base of the fruit-stalk, which are mostly somewhat different in structure from the stem-leaves, are called the _perichæ´tial_ (περἰ, around, χαἱτη, bristle) leaves.

From among the side-fruited or Pleurocarpous mosses we shall select one only, _Hyp´num rutab´ulum_ (Pl. III. fig. 43), which is common on the trunks of trees and on banks.

In this moss, the nodding unequal curved capsule (fig. 45) has a double peristome, resembling that of _Bryum_ (fig. 47). The calyptra is half-cleft, and the lid conical and shortly beaked. The stem is reclining or procumbent, and the pale green imbricated leaves (fig. 41) are ovate and pointed, faintly saw-edged, the nerve becoming indistinct at about the middle. It will be noticed that the cells of the leaf (fig. 48) have the prosenchymatous form, or are elongate with pointed ends; and that the fruit-stalk (fig. 45) is rough with little grains.

_Fructification._--The fruit-producing organs of the mosses are of two kinds, comparable to those of the flowering plants, but with their names changed, as in the case of the ferns; the representatives of the anther being called antheridia, and those of the pistil archegonia. The antheridia may be best examined in _Polytrichum piliferum_ or _commune_, the patches of stems with red rosette-like heads (figs. 25, 26) being readily found in the spring on open heaths. The coloured leaves forming these heads differ in form from those of the stem, being broader and very sharp-pointed, and have received the distinctive name of _perigónial_ (περἰ, around, γνος, offspring) leaves. In the centre of these leaves, which must be separated with mounted needles in a drop of water, the antheridia (fig. 27), forming oblong cellular green sacs, will be seen; and intermingled with them will be found some slender pale filaments, composed of mostly two rows of cells, which are the _paraph´yses_ (παρἁφυσις, a side growth). If the antheridia are quite ripe, they swell somewhat in the water, and from the free or unattached end a very delicate, colourless, cellular mass gradually escapes. If the antheridia are not quite ripe, the mass must be liberated by dissection.

On carefully examining this mass under a high power, it will be seen to consist of very delicate rounded cells (fig. 3 _a_), each containing a coiled filament, revolving more or less rapidly. After a time, these filaments (fig. 3 _b_) escape, so that they may be examined more minutely. They are excessively delicate, and are best seen when dried on the slide. Each consists of a very slender curved filament, with a still finer filament, or cilium, arising from it on each side. These are the spermatozóa or spermatozóids (στἑρμα, seed, ξῶον, animal, εἶδος, resemblance).

In _Funária_ the antheridia (fig. 37) may also be found, by careful examination, in the little green heads terminating some of the stems (fig. 41, of the natural size). In this moss, the paraphyses are inflated at the summit into little knobs, or they are capitate (fig. 37). The pistil-like organs of mosses, or the _archegónia_, from which the capsule is formed, must be looked for in the winter or early spring. They occur in the parts of the stems from which the fruit-stalk subsequently arises, and are surrounded by perichætial leaves, so as to resemble in general aspect the antheridial heads. They are readily found in _Tortula_ and _Funaria_, which are always at hand.

The archegonia (Pl. III. fig. 21) differ in form from the antheridia, being flask-shaped, with a neck and a dilated base. The neck contains a slender canal, and within the base is a special embryonal cell, from which the capsule is subsequently formed. The spermatozoa of the antheridia pass down the canals of the archegonia, and fertilize the embryonal cells; but one archegonium only comes to maturity in each head, the others ceasing to grow, and withering, in which condition they are found at the base of the fruit-stalk when the capsule is fully formed. The embryonal cell grows by subdivision, so as to form a stalk-like body, which as it rises extends the archegonium upwards until it splits across near the base. Thus the archegonium becomes split horizontally into two parts, the upper and longer of which forms the calyptra, whilst the lower remains as a very short tube or sheath (_vagi´nula_) surrounding the base of the fruit-stalk. The cellular stalk-like body then swells at the summit, the swollen portion gradually becoming developed into the capsule, by resolving itself into an outer wall lined inside with a coat forming the outer row of teeth at the top, and within this a thinner membrane or spore-sac, the cleft upper margin of which forms the inner teeth; and within this are contained the spores. The mass of cells within the spore-sac remains, forming a central column, called the _columella_.

These stages of growth may be readily traced in _Funaria_. In Plate III., fig. 40 represents two fertilized archegonia of the natural size, surrounded by the perichætial leaves; fig. 33 is a still more advanced archegone. In fig. 34 the calyptra has separated from the vaginule, and contains the stalk-like body, which is represented alone in fig. 32, the dark summit indicating the commencing formation of the capsule. Fig. 35 represents the young capsule, in which all the parts are more advanced in growth.

When the seeds of mosses germinate, they produce at first a green _Conferva_-like filament, which branches at one end, the cells containing green endochrome, while brownish little roots are given off from the other end. The young leafy buds or young stems arise from these confervoid filaments.

_Examination._--In the examination of the mosses, the capsules should be viewed as opake objects while fixed in the forceps; and to discover the minute structure of the teeth of the peristome, a capsule should be wetted with spirit, then immersed in water, slit up with fine scissors, and spread out with the mounted needles, so as to form a transparent object. In this way, the curious structure of the teeth becomes very distinct.

It must be noticed that, in the mosses, the antheridia and the archegonia usually occur in separate flower-like heads; or the mosses are either monœcious or diœcious (p. 38).

_Preservation._--The mosses may be dried under pressure, and preserved entire in the same manner as the ferns or the flowering plants. If simply dried without pressure, their structure can be readily made out at any future time, by immersing them in water, or by keeping them for a few hours in a moist atmosphere. The minute structures of mosses may be mounted in solution of chloride of calcium, or in glycerine; they keep extremely well without closing the cells.