this structure is the pro-embryo. The cells are at first in a single layer, but the central ones soon become divided by horizontal septa, so as to produce a double layer, and finally, four or more tiers of cells one above another. The outline of the pro embryo, seen from above, is cellular, spreading over the upper part of the spore. On its surface appear the so-called ovules. The first is produced at the apex of the pro-embryo; the rest, to the number of twenty or thirty, arranged upon its surface in thee lines corresponding to the slits by which the outer coat of the spore bursts. These ovules, closely resembling those of Salvinia, Pilularia, the Ferns, &c., consist of a globular cell, surmounted by four cells, which rise up into four papillæ, and leave a canal, or inter-cellular passage between them, leading down to the globular cell or embryo-sac. The four cells are usually developed into four or five cells, one above the other, by the production of horizontal septa; sometimes they are developed unequally, and to a considerable extent, so as to form papillæ, presenting an orifice between them at some point on the outer surface, indicating the canal leading down to the embryo-sac. During the development of the ovules, a delicate parenchyma is produced in the great cavity of the spore, finally entirely filling up this spore. Before it has completely filled it, the embryo makes its appearance in the embryo-sac of one of the ovules. The first change in this sac is the appearance of a nucleus; from this cells are developed representing the suspensor of the embryo. The cells of the suspensor multiply and form the process which penetrates down into the parenchyma of the cavity of the spore; at the lower end may be detected the embryo, a minutely cellular body. Dr. Mettenius never saw the embryo produced in the embryo-sac before the suspensor had broken through the bottom of it to penetrate the parenchyma of the spore-cell; it was always within this parenchyma, and attached to the end of the suspensor. In this point he is decidedly opposed to Hofmeister, who states that the embryo originates in the embryo-sac, whence a young embryo attached to its suspensor may easily be extracted from the spore. The part of the embryo opposite to the point of attachment of the suspensor corresponds to the first axis of the Rhizocarpeæ, which never breaks out from the spore-cell in Selaginella; it pushes back the loose parenchyma of the spore-cell as it becomes developed, and when completely formed, is surrounded by a thin coat composed of several layers of the parenchymatous cells much compressed, enclosed in the still existing inner coat of the spore. On one side of the point of attachment of the suspensor the embryo grows out towards the point where the spore-cell has been ruptured, thus apparently in a direction completely opposite to the end of the axis. As it enlarges, it produces in this situation the leafy stem growing upwards, and the adventitious root turning downwards. The pro-embryo is at first distended like a sac, and finally broken through on the one side by the first leaf, on the other by the adventitious root; upon it may be observed the numerous abortive ovules, with their embryo-sacs filled with yellow contents; part of its cells grow out into radical hairs. Dr. Mettenius several times saw two young plants produced from one spore; the ends of their axes lay close together, and separated inside the cavity of the spore. No account is here given of the characters exhibited by the small spores, or of anything like a process of fertilization; yet there is indicated in the foregoing description of the so-called ovules, a clear analogy between these bodies and the so-called ovules of the Ferns and Rhizocarpeæ. These points will be referred to again at the close of the report. Hofmeister further states that spiral filaments are produced from the small spores of Selaginella, but he does not say that he has seen them, or give any authority. So far Henfrey. Mr. Thuret reports (Recherches sur les Zoospores des Algues, &c. p. 81) that he has often tried to make the spores of L. clavatum and inundatum grow, but could never succeed, any more than with those of Adder's-tongues (Ophioglossaceae), which are very analogous to those of Lycopods. "Must we then conclude," he says, "with M. Spring, that these genera consist exclusively of males? I would prefer to suppose that the true fructification of these plants still remains to be discovered." (See also page 53 d.) ORDER XXII. MARSILEACEÆ.-PEPPERWORTS, OR RHIZOCARPS. Rhizocarpe, Batsch. Tab. Aff. (1802); Agardh Aph. 111. (1822).-Rhizospermæ, Roth. DC. Fl. Fr. 3. 577. (1815).-Hydropterides, Willd. Sp. Pl. 5. 534. (1810).-Marsileaceæ, R. Brown Prodr. 166, (1810); Grev. Fl. Edinens. xii. (1824); Ad. Brongn. in Dict. Class. 10. 196. (1826); DC. and Duby, 542. (1828); Martius, Ic. Pl. Crypt. 121. (1834); Endl. gen. xxxiv.-Salvinieæ, Juss. in Mirb. Elém. 853. (1815).-Salviniaceæ, Bartl. Ord. Nat. 15. (1830); Martius, Ic. Plant. Crypt. 123. (1834); Ed. Pr. Endlich gen. xxxiii.-Isoeteæ, Rich. Bartl. Ord. 16. Endlich. gen. xxxv.-Salvinina and Azollina, Griffith in Calcutta Journ., vol. v. DIAGNOSIS.-Lycopodal Acrogens, with many-celled radical spore-cases, and the reproductive bodies of two different kinds. Stemless plants, creeping, or floating; leaves usually stalked, sometimes sessile and scaly, occasionally destitute of lamina, and rolled up in vernation. Reproductive organs enclosed in involucres, and of two kinds; the one, clustered and stalked, or crowded confusedly without stalks, and distinct from the second, or mixed with it, or in contact with it; the other, simple oval bodies, sometimes having a terminal nipple, from which germination uniformly proceeds. [Stem and leafstalks filled with longitudinal cells. A central simple fascicle of vessels composed of scalariform ducts and prosenchyma, enclosing in the middle a quantity of elongated cells containing starch. Leaves with nerves, veins and stomates.-Martius.] The Order to which Pilularia and Marsilea belong consists of floating or creeping plants, often having the circinate vernation of Ferns, with their reproductive organs in close cases, called involucres, springing either from the root, or from the petioles of the leaves. These involucres contain oval bodies of two kinds, one of which has been called anther, and the other capsule. Figures of Marsilea vestita and polycarpa have been published by Hooker and Greville, at t. 159 and 160 of their noble Icones Filicum. From these, and the more detailed observations of Esprit Fabre, it is clear that the involucre of that genus consists of an involute leaf analogous to the carpellary leaf of flowering plants. Esprit Fabre has also shown, (Ann. Sc. Nat. 2 ser. 7.221, 9. 115 and 381, and 12. 255,) that on the side of a mucilaginous cord, which I regard with Braun as a midrib, proceeding from the involucre when it opens, there arise oblong plates bearing two sorts of bodies packed closely, sometimes intermixed, but sometimes separated, so that each occupies a different side of the plates (which are leaflets). He regards these two sorts of bodies as anthers and ovules, and says, that their mutual position is such, that the side which bears the ovules is above that which bears the anthers. The" ovules" are from 10 to 15 on each side, whitish, semitransparent, ovoid, obtuse at one end, and terminated at the other by a nipple. The "an 3. thers" are little flattened parallelopi- 1 Fig. XLIX. left apart in water they putrefy, while, on the other hand, if mixed together in water, he has seen the sides of the "anthers" burst, and the "grains of Fig. XLIX.-1. Growing plant of Marsilea pubescens ; 2. an involucre opened by 2 valves, from which rises a leaf whose lateral leaflets are loaded with spores; 3. an involucre which bas opened, and from which the sporiferous leaf is disengaging itself; at A is seen the side which Fabre regards as anthers. pollen" collect about the nipple at the surface of the water, after which the "ovules" fall to the bottom, where, at the end of seven or eight days germination commences. These observations, however, require to be repeated; for Braun (Flora, 1839, p. 297,) and Griffith each regards both sorts of bodies as sporules. Fabre's experiment calls to 2 Fig L. thing but abortive spores. mind those of Professor Savi of Pisa, upon Salvinia, another plant of this Order. He put into different vessels, 1st, the seeds alone; 2d, the male globules alone; and 3d, both mixed. In the first two vessels nothing appeared; in the 3d, the seeds rose to the surface of the water and fully developed. But Duverney has since published a dissertation upon this plant, in which he states that, having repeated the experiments of Savi, he has not obtained the same results, and that the seeds, when separated from the supposed male organs, developed perfectly. The structure of Pi- Follo ving Jussieu, Salvinia and Azolla were separated in the last edition of this work as a distinct Natural Order, a view that Endlicher has since taken. But upon a full consideration of the structure of these plants, or of what is known of it, it does not appear to justify the separation. Like Pilularia and Marsilea, they have two distinct kinds of reproductive bodies enclosed in involucres, and that seems to be the main feature by which Pepperworts are known as an Order from Lycopodiaceæ. For the same reason it appears better to combine with them Isoetes, instead of re garding that too as the type of still another Order. Mr. Griffith does not include Isoetes among these plants; but I cannot assent to the propriety of erecting every genus in this curious Order into a Suborder. The genera Salvinia and Azolla have been the subject of some elaborate observations by Mr. Griffith, (Calcutta Journal, vol. v.), who elevates each into a Suborder, and throws an entirely new light upon their structure. He regards them as having true sexes, the male being certain necklace-shaped threads found at an early stage, in contact with what he denominates an orthotropous ovulum. But strange to say, this so called ovulum, instead of giving birth to an embryo, becomes the parent of reproductive bodies of two totally different kinds, having not even the smallest resemblance the one to the other, although the matrix out of which they are evolved is identical at an early period of the organisation. I regret that Mr. Griffith's most curious memoir only reached me as this sheet was going to press, so that it was impossible to have cuts prepared to illustrate his observations, for which the reader is referred to the work above quoted. All I can do is to give in a note the substance of his descriptions of Salvinia and Azolla. LI. Salvinia verticillata.-Male organs? articulated hairs on the stalks of the ovula; each joint containing a nucleus and a brownish fluid: Ovula nearly sessile, concealed by the roots, and partly covered Fig. L.-Marsilea pubescens in different states of germination; advancing from 1. the spore, up to 4. the perfect young plant. Fig. LI.-1. Pilularia globulifera; 2. spore-case, natural size, bursting; 3. the same younger and magnified; 4. a section of the spore-case, showing the large and small spores, (after Valentine). Delile has published an account of the germination of Isoetes setacea, from which it appears that its sporules sprout upwards and downwards, forming an intermediate solid body, which ultimately becomes the stem, or corm; but it is not stated whether the points from which the ascending and descending axes take their rise are uniform. In Pilularia Mr. Valentine finds, that germination takes place invariably from a fixed point. Delile points out the great affinity that exists between Isoetes and Lycopodium, particularly in the relative position of the two kinds of reproductive matter. In Lycopodium, he says the pulverulent spore-cases occupy the upper ends of the shoots, and the granular sporecases the lower parts: while, in Isoetes, the former are found in the centre, and the latter at the circumference. If this comparison is good, it will afford some evidence of the identity of nature of these bodies, and that the pulverulent ones are at least not anthers, as has been supposed; for in Isoetes the pulverulent inner bodies have the same organization, even to the presence of what has been called their stigma, as the outer granular ones; so that, if Isoetes has sexes, it will offer the singular fact of its anther having a stigma. The anatomy of Isoetes is described by Mohl in the Linnæa, xiv. 181. The Pepperworts evidently approach the Clubmosses through Isoetes, which is sometimes referred to the one Order, sometimes to the other. Their genus Azolla appears to bring them into contact with Jungermanniaceae. According to Mr. Griffith, Marsilea evidently appears to connect Salvinia with Ferns; " its important differences from Salvinia consist in the capsules, which correspond to the secondary capsules of that family, being developed within the substance of a modified leaf, in their occurring mixed with each other, and in the spores of the pedicellate capsules not becoming imbedded in apparently cellular masses." All are inhabitants of ditches or inundated places. They do not appear to be affected by climate so much as by situation, wherefore they have been detected in various parts of Europe, Asia, Africa, and America; chiefly however in temperate latitudes. Uses unknown. POSITION. Lycopodiaceae.-MARSILEACEE.-Jungermanniaceæ. with hairs; tegument open at the top; mature reproductive organs solitary, or in racemes of 3-5, about the size of a pea, covered with brown rigid hairs. The upper ongs of each raceme, (or lowest as regards general situation,) contain innumerable sphærical bodies, of a brownish colour and reticulated cellular surface, terminating capillary simple filaments. These again contain a solid whitish opaque body. The other, which occupies the lowest part of the raceme, and which is the first and often the only one developed, is more oblong, containing 6-18 larger, oblong-ovate bodies, on short stout compound stalks: colour brown, surface also reticulated. Each contains a large, embossed, opaque, ovate, free body, of a chalky aspect it is three-lobed at the apex, and contains below this a cavity lined by a yellowish membrane, filled with granular and viscid matter and oily globules. Azolla pinnata.-The growing points present a number of minute confervoid filaments, the assumed male organs, which at certain periods may be seen passing into the foramen, the ovula becoming resolved into their component cells within the cavity of that body; organs of reproduction in pairs, attached to the stem and branches, one above the other, concealed in a membranous involucrum; ovula atropous, oblong-ovate, with a conspicuous foramen and nucleus, around the base of which are cellular protuberances; capsules of each pair either difform-in which case the lowest one is oblong-ovate, the upper globose or both of either kind, generally perhaps the globose, presenting at the apex the brown remains of the foramen, and still enclosed in the involucrum ; upper half generally tinged with red; the oblongovate capsule opens by circumcision; with the apex separate the contents, which consist of a large yellow sac contained in a fine membrane, the remains of the nucleus (or the secondary capsule.) The sac is filled with oleaginous granular fluid, and surmounted by a mass of fibrous tissue, by which it adheres slightly to the calyptra; on the surface of the fibrous tissue are 9 cellular lobes (the three upper the largest), which when pulled away, separate with some of the fibrous tissue, and so appear provided with radicles. The globose capsule has a rugose surface from the pressure of the secondary capsules within; these are many in number, spherical, attached by long capilliform pedicels to a central much branched receptacle; each contains two or three cellular masses, presenting on their contiguous faces two or three radiciform prolongations. In their substance may be seen imbedded numerous yellow grains, the spores. Very full details respecting the structure of this order are given by Mr. Henfrey, whose report is here quoted almost literally : The spores of the Isoëtes lacustris are of two kinds, analogous to those of the Lycopods; both kinds being produced in spore-cases imbedded in the bases of the leaves, but the large spores are found in great numbers, not merely four in a sporangium as in the Lycopods. The development of the spores was little known until the publication of an essay on the subject in 1848, by Dr. C. Müller, forming a sequel to his researches on the Lycopods. Müller compares the complete large spore, as discharged from the sporangium, to the ovule of flowering plants; and he describes it as a globular sac enclosed by three coats, which he names the primine, secundine, and the nucleus. The outermost coat, or primine, is stated to be composed of a thick cellular membrane exhibiting a raised network of lines, which give it the aspect of a cellular structure, but are in reality analogous to the markings on pollen-grains. The outer surface exhibits the lines indicating the tetrahedral arrangement of the spores in the parent cell, as in Selaginella, and it is at the point of intersection of these that the membrane gives way in germination. The next coat, or secundine, is another simple membrane lining the first. The nucleus is a coat composed of delicate parenchymatous cells, but among these are found groups of peculiar character. These are described as consisting of a large cell divided by two septa crossing each other at right angles, projecting from the general surface, being either oval in the general outline, or having four indentations opposite the cross septa, so as to give the appearance of the structure being composed of four spherical cells. The cells surrounding them are of irregular form, different from the generally six-sided cells of the rest of the nucleus. Many of these groups occur on the nucleus, always at the surface of the coat where the primine and secundine afterwards give way, scattered without apparent order over it, but one always near the point of the opening. To these structures Dr. Müller did not attribute any important function, explaining them merely as produced by peculiar thickenings of the tissue to protect the pro-embryo during germination. The contents of the nucleus were stated to resemble those of the cavity of the spores of Selaginella. In these contents, which become dense and mucilaginous, a free cell is developed near the upper part of the cavity; this is the rudiment of the embryo, and by cellmultiplication it becomes a cellular mass, which soon begins to exhibit growth in two directions, producing the first leaf and the first rootlet, projecting from a lateral cellular mass, which the author calls the "reservoir of nutriment." The embryo then breaks through the coats, the first leaf above, and the first root below, the coats remaining attached over the central mass of the embryo. The subsequent changes need not be mentioned here, further than to state that the leaves succeed each other alternately, and are not opposite, as in the Lycopodiacea; moreover, no internodes are developed between them, so that the stem is represented by a flat rhizome, like the base of the bulk of many Monocotyledons. In the paper by Dr. Mettenius, already alluded to, we find some very important modifications of, and additions to, this history of development of the spores of Isoëtes, bringing them into more immediate relation with the other vascular Cryptogams. This author describes the spore-cell as a thick structure, composed of several layers; in some cases he counted four. It completely invests the pro-embryo, which is a globular cellular body filling the spore-cell. Among the cells of the outermost layer of the pro-embryo (which layer forms the nucleus of Dr. Müller), on the upper part, are produced the ovules, fewer in number than in Selaginella, arranged in three rows converging upon the summit of the spore, these rows corresponding to the slits between the lobes of the outer coat of the spore. The four superficial cells of the ovules (which are evidently the peculiar groups mentioned by Müller, and previously noticed by Valentine) grow much in the same way as in the Rhizocarpeæ and in Selaginella, into short papillæ. The embryo is developed in the substance of the pro-embryo, displacing and destroying its cells, and a globular portion (corresponding to the "reservoir of nutrition" of Müller) remains within the spore after the first leaf and rootlet have made their way out. This body is the analogue of that portion of the embryo of Selaginella which penetrates into the cavity of the spore, and to the end of the first axis in the Rhizocarpeæ. The most important point, however, of Dr. Mettenius's researches relates to the phenomenon exhibited by the small spores. In the water in which the spores were sown, he observed moving spiral filaments resembling those of the Ferns. He was not able to trace all the stages of development of these spiral filaments from the small spores, but he obtained nearly all the evidence relating to their origin which Nägeli has done in reference to the similar organs in the Pilularia. In the small |