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The type of Marsileaceæ, properly so called, may be taken from Marsilea itself, of which the most complete account has been given by M. Fabre.
In Marsilea Fabri the fructification consists of a two-valved coriaceous involucre (sporocarpium, Endl.), having its valves held together by a central line continuous with the stalk : this involucre seems to be a modified leaf. From the stalk there rises a mucilaginous ring, to which adhere minute ramifications of the spike, terminating in oblong spikes covered with fructification. After a time the mucilaginous ring detaches itself from the stalk at one end, straightens, and carries up with it the spikes of fructification, whose connection with the stalk is then destroyed. The spil
The spikes are at first enveloped in a mucous membrane, and are composed of two sorts of bodies closely packed together, and considered by M. Dunal to be ovules and anthers. These bodies are sometimes intermixed, sometimes stationed separately from each other. The so called ovules are little white semitransparent bodies, surrounded by a sort of projecting hood, beyond which a narrow papilla projects: this papilla is always turned towards the anthers. The latter are little flat parallelopipedons, rounded at the two ends ; they consist of a membranous sac of great tenuity, in which are found numerous grains of spherical or elliptical pollen. (Ann. Sc., n. s. vii. 227. t. 12, 13.) M. Fabre is represented as having proved experimentally that the latter impregnate the former; and he has traced the ovules from their first impregnation to their completion, and seen and described their germination. (Id. ix. 115. t. 13.) It appears that no trace of embryo is discoverable in the ripe seed.
In the second section of this order, to which the name Salvinieæ may be given, and which consists of the genera Salvinia and Azolla, we find at the base of the leaves membranaceous involucres of two sorts, and containing different organs.
One kind includes a bunch of cases (sporangia, Martius), containing only one grain in Salvinia, and from six to nine in Azolla. The integument of these cases is thin, reticulated, brownish, and does not swell in water like that of true Marsileacew: the pedicle which supports them appears,
in Salvinia, to communicate laterally with the case. The other involucres, which are supposed to be male organs, have a very complex structure, and have been well observed by Brown. In Salvinia they contain a great number of spherical granules, attached by long pedicles to a central column : these granules are much smaller than the grains; their surface is reticulated in like manner, and they do not burst by the action of water. All the species are floaters, and their leaves are not gyrate when developing, but are more like those of Lycopodiaceæ. Thus far Brongniart; see also Martius, Ic. Pl. Crypt. Bras., for many curious additional observations.
With respect to the nature of these two kinds of grains or granules, it has been thought, as is obvious from the foregoing remarks, that the smaller are males and the larger females ; which has been supposed to be proved by the experiments of Savi of Pisa. This observer introduced into different vessels, 1. the granules; 2. the grains; and, 3., the two intermixed. In the first two nothing germinated; in the third the grains floated to the surface and developed themselves perfectly. These observations have, however, been repeated by Duvernoy without the same result. But M. Fabre's observations upon Marsilea seem to leave little doubt about this order having reproductive organs analogous to sexes.
5. Mosses and Andræaceæ.
In the structure of these plants neither vessels nor woody tissue are employed; and henceforward those organs disappear from the structure of all the orders to be noticed. Their stem consists of elongated cellular tissue, from which arise leaves composed, in like manner, entirely of cellular tissue without woody tissue; the nerves, as they are called, or, more properly speaking, ribs, which are found in many species, being formed by the approximation of cellules more elongated than those which constitute the principal part of the leaf. The leaves are usually a simple lamina; but in Polytrichum and a few others they are furnished with little plates called lamellæ, running parallel with the leaf, and originating in the upper surface.
At the summit of some of the branches of many species are seated certain organs, which are called male flowers, but the true nature of which is not understood. They are possibly organs of reproduction of a particular kind, for both Mees and Haller are recorded to have seen them produce young plants. Agardh says they have only the form of male organs ; and that they really appear to be gemmules. By Hedwig they were called spermatocystidia ; by others staminidia or antheridia. They
They are cylindrical, articulated, clavate, membranous bodies, opening by an irregular perforation at the apex, and discharging a mucous granular fluid. Among them are found slender, pellucid, jointed threads, which are abortive antheridia. Unger and Meyer have found spermatic animalcules, apparently Vibrios, in the antheridia of Sphagnum and Hypnum. (Comptes Rendus, vi. 632.)
But, whatever may be the nature of these organs, there is no doubt of the reproductive functions of the contents of what is named the sporangium, theca, or capsule, which is a hollow urn-like body, containing sporules : it is usually elevated on a stalk, named the seta, with a bulbous base, surrounded by leaves of a different form from the rest, and distinguished by the name of perichætial leaves. If this sporangium be examined in its youngest state, it will be seen to form one of several small sessile ovate bodies ( pistillidia, Agardh; prosphyses, Ehrhart; adductores, Hedwig), enveloped in a membrane tapering upwards into a point; when abortive they are called paraphyses. In process of time the most central of these bodies swells, and bursts its membranous covering, of which the greatest part is carried upwards on its point, while the seta on which the sporangium is supported lengthens. This part, so carried upwards, is named the calyptra : if it is torn away equally from its base, so as to hang regularly over the sporangium, it is said to be mitriform; but if it is ruptured on one side by the expansion of the sporangium, which is more frequently the case, it is denominated dimidiate. When the calyptra has fallen off or is removed, the sporangium is seen to be closed by a lid terminating in a beak or rostrum : this lid is the operculum, and is either deciduous or persistent. If the interior of the sporangium be now investigated, it will be found that the centre is occupied by an axis, called the columella ; and that the space between the columella and the sides of the sporangium is filled with sporules. The brim of the sporangium is furnished with an elastic external ring, or annulus, and an interior apparatus, called the peristomium : this is formed of two distinct membranes, one of which originates in the outer coating of the sporangium, the other in the inner coat; hence they are named the outer and inner peristomia. The nature of the peristomium is practically determined at the period of the maturity of the sporangium. At this time both membranes are occasionally obliterated ; but this is an unfrequent occurrence: sometimes one membrane only remains, either divided into divisions, called teeth, which are always some multiple of four, varying from that number as high as eighty, or stretching across the orifice of the theca, which is closed up by it; this is sometimes named the epiphragma or tympanum. Most frequently both membranes are present, divided into teeth, from differences in the number or cohesion of which the generic characters of mosses are in a great measure formed. For further information upon the peristomium, see Brown's remarks upon Lyellia, in the 12th volume of the Linnean Transactions.
M. Endlicher considers that the sporangium is formed by the adhesion of an external and internal series of organs; and he calls sporangidium the inner, to which the peristomium belongs. (Genera Plantarum, 46.)
The interior of the sporangium is commonly unilocular; but in some species, especially of Polytrichum, it is separated into several cells by dissepiments originating with the columella.
If at the base of the sporangium there is a dilatation or swelling on one side, this is called a struma ; if it is regularly lengthened downwards, as in most of the Splachnums, such an elongation is called an apophysis.
In Andræaceæ the sporangium is not an urn-like case, but splits into four valves, cohering by the operculum and base.
The spores have no adhesion either to the sides of the sporangium or to the columella, but appear to be formed much in the same way as pollen. When they germinate they produce capillary, articulated, green, branched threads, resembling Confervæ; and the leaves eventually appear from the axils of such branches.
From the foregoing description, it will be apparent that the organs of reproduction of Mosses cannot be compared strictly to the parts of fertilisation of perfect plants. I must not, however, omit the opinion of other botanists upon this subject. The office of males has been supposed by Micheli to be performed by the paraphyses; by Linnæus and Dillenius, by the sporangia; by Palisot de Beauvois, by the sporules ; by Hill, by the peristomium ; by Kælreuter, by the calyptra; by Gærtner, by the operculum; and, finally, Hedwig has supposed the males to be the antheridia. The female organs were thought by Dillenius and Linnæus to be assemblages of antheridia; by Micheli and Hedwig, the young sporangia ; and, by Palisot de Beauvois, the columella.
For some suggestions as to the analogy that is borne between the organs of Mosses and those of other plants, see MORPHOLOGY hereafter, and Endlicher's Genera Plantarum.
6. Jungermanniacea and Hepatice.
These differ remarkably from each other in the modifications of their organs of reproduction, while they have a striking resemblance in their vegetation. This latter, which bears the name of frond or thallus, is either a leafy branched tuft, as in Mosses, with the cellular tissue particularly large, and the leaves frequently furnished with lobes, and appendages at the base, called stipulæ or amphigastria ; or it is a flat lobed mass of green vegetable matter lying upon the ground.
In Jungermannia, that part which is most obviously connected with the reproduction of the plant, and which bears an indisputable analogy to the theca of Mosses, is a valvular brown case, called the capsule or conceptacle (sporangium or sporocarpium), elevated upon a white cellular tender seta, and originating in a hollow sheath or perichætium arising among the leaves. This conceptacle contains a number of