tants eagerly profited by the occasion, and made it into b 3 In stating this fact for your information, I would pray The analyse them, and favour me with your opinion upon ret tible grains enclosed in the letter were the grains of the come Lichen the Lecanora esculenta now under consideration. What then is the internal organisation of Lichens P 7

These Thallogens, when perfect, consist of a nutritious pine tative apparatus designated the thallus, and of double reprodne® organs. A thallus, which is sometimes imperceptible, may acer attain the length of ten yards. The colours which it pais or presents are white, grey, yellow, citron, orange, BE: =black. As to its ' form, it is foliaceous in Parmelia;

in the Usneas; crustaceous, as in the Squamaria; hypophleod, or hidden under the epidermis of the trees, or under the woody fibres, as in the Verrucaria, Xylographa, &e.

In order to give some idea of the anatomical structure of the _ thallus, it will suffice to mention Parmelia parietina, the thallus of which does not exceed the three-hundredth part of an inch in thickness. Thin as it is, however, this organ presents four very distinct regions. Its upper part consists of a bed of thick closely consolidated cells, of a yellowish colour at their surface only. In front of the lower part of the thallus is another cellular bed, white, like the first. Between these two epiderms are confined, Ist, the green seeds known as gonidia, and formed of a bed called gonidial; 2nd, a kind of medulla, or pith, formed of filamentous elements loosely interlaced or knitted, which is the medullary bed, and Which encloses the air in the mesh.

If we pass from the vegetative to the reproductive system, we find that it consists of the fructifying or female organs, and a fecundating or male apparatus; the first being represented by the Apothecceia—namely, the cups or shields containing the fructification; the second by the Spermogonia.

The apothecceia of fruits of the Lichens develop themselves on the upper face of the thallus, or upon that part of it which is turned towards the light. They strongly resemble the small disk or nucleus—black, brown, yellow, rose-coloured, red, and sometimes interspersed with brown or grey. In size they are extremely Variable;the smallest are under the one-twentieth of an inch, whilst the largest may be an inch. The Spermogonia are generally very small organs, rounded or oblong, lodged sometimes in particular tubercles, but more * frequently immerged in the superficial beds of the thallus. _ re Y reasons lead to the conclusion that the spermogonia are ®male organs of the Lichens. At first they present themselves Parallel in the fruit, or simultaneously with it in the same individual, at other times only upon sterile individuals in such a manner th. Mm the latter case the apothecceia and the spermogonia develop The tenuity of the cor- “mselves upon different individuals.

Contained in the spermogonia, their immense numbers

relatively to the number of their spores, their solidity, their form, their equality as to size, the absence of all germinating faculty, are so many circumstances which seem to identify them with the attribute of being agents of fecundation analogous to the antherozoids of other Thallogens. But they possess, so far as is known?, no organs of locomotion. Crass IT.—Acrocens. So-called from their stems growing in height and not in diameter. They are flowerless’ plants, like Thallogens, the stems and leaves of which are distinguishable, and in other respects they approach closely to higher structural forms, even acquiring the stature of lofty trees in some of the orders. They have breathing pores, or stamate, on their surface; their leaves and stems are distinctly separated in most of the species; in some of them the spiral spermatoids, which form an important portion of the internal anatomy of the higher forms of vegetation, are found well developed, and they are propagated by reproductive spores, but without any direct evidence that Acrogens possess organs requiring to be fertilised, the one by the other, in order to be a ae The Acrogens correspond with the Acotyledons of De Jussieu, an the Cellulares of De Candolle. | Sub-class | Characteristics | Orders | |---|---|---| | 4. Muscals | Cellular, sometimes vascular. Spore cases plunged in the substance of the frond, or enclosed in a hood which serves as an involucre to the seed vessels. | XV. Ricciaceæ, crystal worts; XVI. Marchantiaceæ, or liverworts; XVII. Jungermaniaceæ, scale mosses; XVIII. Equisetaceæ, or horsetails; XIX. Andræeæ, or split mosses; XX. Bryaceæ, or urn mosses. | | 5. Lycopodals | Vascular, with axillary or radical spore-cases, one or many-celled, spores of two sorts. | XXI. Lycopodiaceæ, or club mosses; XXII. Marsilleaceæ, or pepper worts. | | 6. Filicals | Vascular with marginal or dorsal spore-cases, one-celled, usually surrounded by an elastic ring spore of one sort. | XXIII. Oppioglassaceæ, or adders’ tongues; XXIV. Polypodiaceæ, or ferns; XXV. Danæaceæ, or Danæads. |

Of the Muscals, Hepaticals or Liverworts have a loose cellular texture, usually prostrate, and producing rootlets in their sides: they grow in damp places. Sometimes the stem and leaves unite and form a confluent expansion; in other cases the leaves are distinct from the stem. “The most remarkable points of structure in Hepaticæ,” says Dr. Lindley, “is the spiral filament, as it is called, lying among the sporules, within the theca or sporule case, and having a strong elastic

force. This consists of a single fibre, or two twisted spirally in different directions so as to cross each other, and is con-perishable tube.” This tained within a very delicate transparent or Liverworts, which root on Marchantiacea, order contains the—I. the ground, on walls, rocks, and damp places; II. Ricciacee, float-immersed in fructification ing plants, rooting on the ground, their membranous the frond. III. Anthoceratew, annuals with fleshy or fronds, spore cases raised on a pedicel, two or three inches long, Jungermaniacee, frondose or with a free central columella. IV. foliaceous plants, spore cases opening with four valves, spores mixed with elaters.; The structure of the plants, some of them of microscopic minute- They are furnished with leaves, interesting. ness, is singularly arranged over a distinct axis of growth; and their reproductive organs are of two kinds, the most general being the urn sporangium’ or theca, in which the spores or seeds are generated. If examined in the season of growth, it will be observed that some of the axils of the leaves contain clusters of articulated filaments, swollen at the base, some of them being larger than the others. After a while coating, which membranous this body is found to have an exterior Separates from the base in a cup-like form; this is the young urn, which gradually acquires a stalk called the seta, upon which it is raised above the leaves carrying the other membrane upward on its . Point, covered, when full grown, with a cap, called its ca/yptia. the urn is closed by a lid, its operculum, and contains the spores Its rim is or columella. column, central surrounding ma cavity called the processes, bordered by a double set of teeth, like jointed beristoma. A second set of organs called Antheridia are observed, which - also form clusters in the axils of the leaves; they are membranous out at opening irregularly bodies, or jointless, jointed, cylindrical a mucous turbid fluid. Now the func- the Point and discharging tion of these two sets of organs has long been a subject of dispute. The discovery of the two kinds of organs, the Antheridia and and the analogous spiral Pistillidia, in the Mosses and Hepaticess, a sexual orga- _ to indicate were supposed in the Characee "ments . nisation. Professor von Mohl pointed out the analogy between the and or Thallogens Cryptogamia of the spores of the clopment

the pollen-grains of the flowering plants, but considerable obscurity still surrounds the question. Mr. Valentine traced an evident analogy to ovules in cells closely resembling the parent cells of pollen and spores. While Schleiden thought he observed fertilisation of the supposed ovules by the smaller spores. The view 20W entertained by the best authorities as to the reproduction of the mosses is that the Antheridia are male organs which by means of the spiral filaments exert a fertilising influence upon the Pistil-idia. But no such fertilising process has actually been observed in the mosses, the evidence being only circumstantial.

THE Mosszs. The Mosses, which now number not less than ten thousand species, are humble plants, but they have no insignificant part t0 play either in the economy of Nature or in the physiognomy of the landscape. ‘Trees, walls, rocks, and ruins assume a smiling picturesque aspect under their mossy covering in its varied colours. The Phascum, growing in the gravelled alleys of woods and gardens, are so very minute that in some cases they scarcely attain the height of the hundredth part of an inch. The Hypn™ which often clothe the banks of brooks in shady places, oF sare small islets at the foot of willows and poplars, or attached ae ey trunks of these trees, are vigorous vegetable organisms which do not readily perish. The Fontinalis are small grass-like mosses

|which float in the middle of running brooks. The Sphagnums grow

in marshy places, where they perform an important part in ge”

‘3tion of bog turf. These aquatic mosses grow very rapidly, exten to ing their roots in such a manner as to occupy by degrees the ide interior of the pool which they occupy. Their thin and delica tissues absorb more than sixteen times their weight in water; ®” when they die they accumulate in the bottom of the water, me form with mud and the detritus of other plants a mixture fo; when consolidated by time, is cut out in oblong squares, ee the name of peat-turf forms an important article of domesti¢ si im some countries.: of The Polytrichum, commonly called the golden moss, 18 0R° the most elegant of its kind; it is larger than the common

(273 ACROGENS.

and grows generally among heaths, in fir woods and bogs. Its principal stem creeps along the ground, throwing out from time to time adventitious roots, which penetrate the soil, throwing out branches to the surface. These branches carry the leaves, are narrow, lanceolate, or awl-shaped, and finely dentate or serrated on their edge; imbricate in a spiral form round the stem; the leaves of the lower part assume a reddish colour at maturity.

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ma Sse

eee. A n= ee “xc Ls]

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Fig. 396.—Polytrichum. he 336 the stems terminate, as we see in Nos. 1 and2, by § reddish filament carrying a pointed or cone-shaped cap wackUt © Waist See et yh Spd

Yellow colour. If this cap is raised (see No. 6) we see that it is the cover of an urn-shaped vessel, which contains a prismatic body (No. 9) furnished with a species of covering (No. 8), seated upon a small ledge which is circumscribed by a very thin ridge of greyish colour. field horizontally, the ledge is composed of small pointed teeth curving towards the interior, and connected by a horizontal skin. There are sixty-four of these teeth. As to the interior of the prismatic body, it is hollow, and encloses a multitude of small greenish granules, perfectly free, and which make their escape with great facility when the urn bursts. There is every reason to believe that these granules reproduce the species by germination. There are certain other seeds, but their organisation is so simple, and show so little resemblance to the seeds of the higher orders of plants, that they are called spores. These are enclosed in the interior of a membranous sac, which covers the walls of the prismatic body, and adheres to a central axis called the columella. This prismatic body, in fact, is the w” of the mosses. The free edge of the urn crowned by the teeth 18 the peristomium; here the peristome has sixty-four teeth. The covering reposing on the peristome bears the name of operculum. The cap of yellow hair which shelters the urn almost entirely 18 the calyptra. F inally, the filament which contains the stem and supports the urn is the theca. Of this nomenclature, Dr. Lindley m the Outlines of Botany remarks, that to the uninitiated it requives explanation, otherwise it might be supposed to apply to some vegetoanimal. “The calyptra,” he says, “may be understood to be 4 convolute leaf; the operculum another; the peristomium one more whorls of minute flat leaves; and the theca itself, the excavated distended apex of the stalk, the cellular substance of which separates in the form of sporules.”’ This urn, then, results from the development of a small apparat™ bearing a strong resemblance to a long-necked bottle, which - traversed very perceptibly in its entire length by an open cane, expanding at the summit in such a manner as to present ~ analogy with the pistil of plants of higher organisation, and whi¢ has been called an archegonium. At first many archegones 9F° enclosed in the terminal rosette of the stem (as in 3 and 7, Fig. 336), but only one of these is ultimately developed into the urn borne at the summit of the theca. | ins ratus

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