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hold equal rank with Mosses and Hepaticæ; the three classes, Bryinæ, or frondose mosses, Sphagninæ, or bog mosses, and Hepaticinæ, or liverworts (the Laubmoose, Torfmoose, and Lebermoose of the Germans), thus forming one great muscal alliance.
As it may be of interest to know something of the histology of the Sphagnums, and except the late Mr. Wilson's admirable sketch of the family in 'Bryologia Brit.' we have little in our own language bearing on the subject, I purpose on this occasion to point out the chief characters which distinguish them from mosses, and at a future time, with your permission, give an account of all the British species, with illustrative figures of their structure.
Commencing with the spore, we find that on germination it does not produce the much-branched confervoid prothallium of mosses, but if growing on the wet peat, a lobed foliaceous production results, exactly like one of the frondose Hepaticæ, as Anthoceros, and from this the young plants grow. This was first observed by Hofmeister in 1854. If germination occur in water, the prothallium is a fine filament, the lower end of which forms roots and the upper enlarges into a nodule from which is developed the young plant. As soon as branches form on the plants, in both cases the prothallium and roots wither away. Next, the stem, which in mosses consists of uniform texture throughout, is in Sphagnums much more differentiated, for we observe-1st, a medulla, or central pith, of long cylindric cells by which a current of sap is constantly passing to the growing apex; 2nd, a woody cylinder of firmer prosenchymatous cells; and 3rd, an outer, or bark-layer of one to four strata of thin walled cells, always larger than the rest, and which in S. cymbifolium alone contain spiral threads and foramina. The branches also are quite peculiar, and differ altogether in arrangement from those of mosses. In the young state they are crowded into a capitulum at the top of the stem, and as the internodes elongate they become separated, and are then seen to be in lateral fascicles of three to ten, the bundle originating at one side of a leaf base, every fourth leaf in the spiral giving rise to a branch fascicle.
Of these branches, one part spread out horizontally and then arch down, the rest being attenuated, pendulous, and pressed back to the stem, and by these water is conducted to the very apex; indeed, Professor Schimper compares their action to a hydraulic pump, for a tuft of plants placed dry in a flask of water immediately carry on the fluid by the lower bark cells, and empty the flask by a discharge of drops from the down-bent capitulum, but if some of the branches and bark be removed, no passage of fluid takes place beyond the injured part.
Of the sponge-like retention of moisture by Sphagnums, we have often unpleasant experience when stepping on the green turf-like surface of its beds, only to plunge deep into their interior, and emerge soaked with the water concealed therein. They can also absorb atmospheric moisture and transmit it downward, thus taking up again at night what they had lost during the day; and by this perpetual interchange the stagnant pools in which they flourish never become putrid. The bark of the branches consists only of a single layer of cells in communication with the innermost layer of the stem bark; but these are of two forms, for besides the ordinary kind, there are others of a flask shape, larger, and with a circular orifice, one of which always falls at a leaf-insertion.
The leaves of bog mosses are very peculiar, and are well known as an elegant microscopic object; those of the stem are more remote from each other than in mosses, and in all the species two complete spirals contain five leaves (phyllotaxy }); their form is ovate or tongue-shaped, with the base frequently more or less auricled. Those of the branches are much narrower, and not only vary on the two forms of branch, but on different parts of each. If we look at a Sphagnum leaf in fluid with a sufficient power, the first thing that strikes us is the beautiful sigmoid form of the areolation, or cellular network; and next, the presence of a delicate fibril forming spirals or rings on the inner wall of each cell, and by which the thin membrane is kept expanded, while perforating the membrane are distinct apertures or pores through which it is common enough to find infusoria have passed, which may be seen sporting about in the cell cavity; and thirdly, that these large prosenchymatous cells are always void of chlorophyl, and hence want the lively green colour so noticeable in true mosses.
This, however, is not all. A more careful examination will show that between the walls of these hyaline cells are placed extremely narrow parenchymatous cells, which do contain chlorophyl. Moldenhawer first detected these in 1812; yet Carl Müller, in his Synopsis Muscorum,' terms them intercellular ducts; in nó case is there any approach to the formation of a nerve or midrib. According to the colour of the chlorophyl in these parenchym cells, is the colour of the Sphagnum tuft, only seen, indeed, in the living or moist state, but presenting endless shades of rosy red, purple, vinous red, bluish green, olivaceous, apple-green, and straw colour. When dry or dead, the hyaline cells lose their transparency, and all the species become more or less a dirty white. The spiral threads are nothing but thickenings on the inner wall of the cell membrane, such as occur frequently in the tissues of phænogamous plants; in one species only are they altogether absent, viz. the American 8. macrophyllum, which Professor Lindberg separates as the genus Isocladus.
The male flowers of Sphagnums differ also from those of mosses, and in their arrangement, and the form of their antheridia, resemble those of Hepaticæ; they are grouped in catkins at the tips of lateral branches each of the imbricated perigonial leaves enclosing a single globose antheridium on a slender pedicel, which is inserted at the side of the leaf base. Paraphyses surround them, but instead of being simple, as in mosses, they are very long, much branched, and of cobweb-like tenuity.
The perigynium of the female flower-sheath terminates one of the short lateral branchlets at the side of the capitulum, and is of a deep-green colour, with large sheathing leaves; the archegonia do not differ from those of mosses.
After impregnation the fruit receptacle enlarges and extends itself into a pseudopodium, on which the capsule is sessile; the vaginula was thought to be absent from these plants, and hence Bridel formed for them a section “Musci evaginulati.” It is, however, very distinct, being the disk-shaped enlargement at the apex of the receptacle in which the expanded bulbous rudiment of the pedicel of the capsule is completely buried.
The calyptra, or outer cell-layer of the archegonium, has not the definite form common to mosses, but is a very thin colourless membrane closely investing the capsule, by the enlargement of which it is torn irregularly into shreds, the lower portion being left attached to the vaginula.
The capsule up to maturity remains in the perichætium, but after that the receptacle elongates and carries it upward on this pseudopodium, which does not correspond to the pedicel of a moss, that being always found above the vaginula ; still, a pedicel does exist in Sphagnum, but it is bulb-shaped, and enveloped by the vaginula. The capsule itself is very uniform in all the species, being almost spherical, the lid only slightly convex, without any beak or point, and we never find any trace of a peristome. The sporangium, or spore sac, does not attain the development found in mosses, for it appears like a hollow hemisphere in the interior of the fruit, its outer wall being coherent with the inner cell-layer of the capsule, its inner wall with the columella lying beneath it.
The spores somewhat resemble those of Lycopods in being of two kinds—macrospores produced by fours in a mother cell and tetrahedral in form, and microspores which are more spherical, and not half the size.
With respect to the function of these plants in the formation of peat, I cannot do better than quote Professor Schimper's words. He says :-“ Unless there were bog mosses, many a bare mountain ridge, many a high valley of the temperate zone, and large tracts of the northern plains, would present an uniform watery flat, instead of a covering of flowering plants or shady woods. For just as the Sphagna suck up the atinospheric moisture, and convey it to the earth, do they also contribute to it by pumping up to the surface of the tufts formed by them the standing water which was their cradle, diminish it by promoting evaporation, and finally, also by their own detritus, and by that of the numerous other bog plants to which they serve as a support, remove it entirely, and thus bring about their own destruction. Then, as soon as the plant detritus formed in this manner has elevated itself above the surface water, it is familiar to us by the name of turf, becomes material for fuel, and all Sphagnum vegetation ceases."
Little noticed, then, as these plants may be, they perform functions in the economy of nature which cannot be overlooked ; and it is for the purpose of inviting more general observation of their structure that I bring forward these remarks. Some seventeen British species are known, all of which I hope to illustrate; and in carrying out this object, I shall feel thankful for good specimens of any of our species, but especially those occurring in the north of Scotland, for the wild moorlands of Northern Europe bave so far proved to be the most prolific in new species.
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II.-Structure of Podura Scales.
By F. H. WENHAM, Vice-President R.M.S. MR. MOINTIRE has kindly presented me with a number of slides ; two of them are superb specimens of the test Podura, L. curvicollis, with markings remarkabīy dark and distinct. In one of the best scales there is a singular case of fracture, evidently caused by the slipping of the cover, which has dragged the specimen asunder near one-third from the upper end, which is separated to a short dis
tance. Projecting from the largest portion is a fragment, partly torn away, as shown by the accompanying cut, which is an outline sketch taken by the camera lucida, 4000 diameters. On the right-hand extremity the longitudinal tear has taken place close to a rib, or marking,
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lated. The transverse tear at the bottom leaves most of the ends of the ribs exposed and projecting, as the membrane has torn away from behind them. The extremities of ribs 4 and 5 (counted from the right) are particularly plain and prominent. I am willing to submit this specimen to the inspection of anyone doubting the fidelity of the tracing.
How it can be maintained or admitted that these waved or constricted ribs which give rise to the “note of exclamation ” markings are “illusory," I am at a loss to imagine. The question can only be determined by fragmentary pieces; but in the Poduræ, from the toughness and absence of brittleness in the scales, these are very difficult to obtain, and it is seldom that a fortunate accident occurs in the way shown.' It was by fragments that the structure of the diatoms became known, wherein the silicious nodules could be traced down to a single atom, and their form is not now a question of dispute.
Mr. Hennah, and others, have demonstrated how a number of different patterns, not the least indicative of real structure, may be produced by transparent bodies of regular form, such as glass rods and bosses, &c. Much more incomprehensible would these appearances be if the transparent ribbings were twisted, lobated, or in the peculiar form of a Podura marking. The patterns would be innumerable with oblique light, and the whole area might be made to
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