71. Our limits will not permit us to enter upon the history of the development in other families of Hepaticm. In the higher Jungermannim, which are provided with a distinct stem, as well as with regularly formed and symmetrically arranged leaves, it closely corresponds to that of Pellia. In the Mar chanties, in which we have ag,ain a frondose stem, we have considerable differences. The antheridia are found on special receptacles of various forms, sometimes stalked capitula, concave superiorly, like the stalked apothecia of some Lichens (Marchantia polymorpha), sometimes sessile. However much the general form may vary, they agree in their relation to the antheridia. These last are flask-shaped bags, and always completely im mersed in the parenchyma subjacent to the upper surface of the receptacle. This surface is always found to be scattered over with nipple-shaped elevations. At the summit of each an aperture is observable—the termina tion of the long and narrow neck by which the cavity of the antheridium communicates with the surrounding medium. The fully formed antheridiurn consists of a central mass of quadrangular cells, which, surrounded by a single layer of others much larger and of a tabular form, is continued upwards so as to forrn the narrow neck ; the whole being closely invested by the parenchyma of the receptacle. Within each of the central cells is found a lentil-shaped vesicle containing a spiral filament, which only differs from those described already, in its greater minuteness. The archegonia of INIarchantia are produced on the under surface of a somewhat umbrella shaped, deeply lobed, stalked receptacle. This body corresponds in the mode in which it takes its origin from the notch in the anterior margin of the frond, with the ordinary vege tative shoot, of which it is obviously a modifi cation. Its development has been well de scribed by M. Mirbel.* The structure of the archegonium, and the commencement of the development of the fruit, correspond very closely with what has been described in Pellia. The mode of formation of the spores and elaters differs, however, considerably. The latter, which in thelast-named plant, are nothing more than fusiform septate cells, attain in Marchantia, as well as in many Jungermannim, a more complicated structure. Their develop ment has been described in an admirable con tribution by Mr. Henfrey, who finds that the young elaters are, like those of Pellia, elon gated fusiform tubes, and contain at first only colourless protoplasma.± Soon after starch granules are deposited in their interior, and they are converted by a growth which is much more rapid in length than in breadth, into very slender, hollow filaments, attenuated at each closed extremity. Still later, the starch and protoplasma disappear, and at length faint streaks, denoting the nascent fibres, are to be perceived upon the walls. These become gradually more and more distinct, till, in the mature elaters, they present themselves a.s strong flattened bands. In Marchantia there are two fibres, which coil in opposite direc tions, and are confluent by their ends at the extremities of the tubes in which they are contained. At the time of the scattering of the spores the cell-membrane gives way, and the elastic fibre rapidly uncoils, at the same time lengthening considerably. The parent cells of the spores in INIarchantia are also, at an early period, fusiform. They are arranged side by side with the young elaters, from which they differ in being very much broader. Each of these cells is converted, by the forma tion of transverse septa, into a series of four, which afterwards separate from each other. In each of the new cells, the protoplasma in creases in quantity and assumes a yellovr colour. Still later it begins to accumulate into four distinct masses, each of which be comes invested in a cellulose membrane, and, after the solution of the membrane of the parent cell, assumes the structure and appear ance of the ripe spore.
72. Mosses.—The Mosses are distinguished from the leafy Hepaticm, first, by differences in the structure and arrangement of the stem and leaves, involving greater complexity ; secondly, by the fact that the leafy axis is not developed directly from the spore, but, with the inter vention of a confervoid structure (proto nema),* resembling in all its relations to the future plant, the mycelium of the Fungi and Lichens.
73. First period.—Gernzination of the spore.t —The spore of the Mosses is a nucleated cell, the solid contents of which are granular, and consist of protein compounds, starch and dex trine. From the budding out of its membrane, results a hollow filament, which, as it lengthens, divides by a succession of transverse septa.
It then begins to branch in all directions, each branch resembling the parent, and rami fying in the same manner. Hence results an entangled network of filaments of a brilliant green colour, which spreads over the moist sreace on which the spores have been sown. At length some of the filaments are observed to give off' lateral branches which differ from those previously formed in being more slender and containing less chloroph3lle. In some of these the terminal cell, after dividing four or five times, becomes globular, and is transformed into the rudiment of a leafy axis.
74. Development of the antheridia and arch. gonia. — These organs are usually found in groups, which are situated either at the termi nation of the stem or branches, or in the axils of the leaves. In either case they are surrounded (with the exception, in many genera, of the axillary antheridia) by special arrangements of modified leaves (involucres). Those involucres which surround the antheridia are called perigonia, and are composed of leaves much smaller than the ordinary leaves of the stem. Those leaves which enclose the archegonia, small at first, attain a large size as the fruit approaches maturity. In some (hermaphro dite) mosses, both antheridia and archegonia are contained in one involucre.
75. In the very diminutive plants belonging to the genus Phascum, which we select as ex amples on account of their great simplicity of structure, the groups of archegonia are termi nal, those of antheridia usually axillary. The growing extremity of the stem (terminal bud) or axillary bud, when destined to bear repro ductive organs, instead of developing to a new axis, becomes flattened in such a manner as to present a slightly convex disc, which takes the place of its conical growing extremity. It is upon the surface of this disc that the rudi ments, whether of antheridia or of archegonia, originate, by a process precisely similar to that which we have described in the commencing development of the antheridia of Anthoceros. The rudiment consists, as in Anthoceros, of four columns of cells, combined so as to form a cylindrical club-shaped body. The development and ultimate form of the arche gonium corresponds so completely with what has been described in the Jungermannim, that it is unnecessary to describe it. The fully formed antheridium of Phascum is a club shaped body of about the same length as the archegoniurn, and consists of a central mass of minute quadrangular cells, which is enclosed by a single layer of tabular cells, in contact with each other by their edges. Shortly be fore the antheridium arrives at maturity, the quadrangular cells, each of which contains a spiral filament enclosed in a lentil-shaped vesicle, are dislocated. This is followed by the total disappearance of their membranes, so that the vesicles float free in the cavity of the now ripe antheridium. No sooner is this the case than the organ gives way at its summit, and discharges its contents in the form of an intestine-like coil of mucus, consisting of the lenticular vesicles with their contents. Soon after, this is dissolved, and the spiral filaments commence their active motions.
76. Development of the fruit. — The early stages correspond with those described in Pel lia. At a period when the lower dilated portion of the archegonium is about five:times its ori ginal length, the young fruit, which is a fusiform cellular body, does not occupy more than its upper half. In the meantime the cells form ing the tissue subjacent to, or in the immediate neighbourhood of, the base of the fructified archegonium, have multiplied with such acti vity, that the end of the stern has again assumed the form of a cone, on the summit of which the fruit is borne, while the aborted archegonia are scattered round its sides. In its further development, the fruit grows much more rapidly in length than in breadth, and in con sequence of its extension upwards being op posed by the resistant structure of the canal of the archegonium, its lower end presses downwards in such a manner as to cause the absorption, not only of the cellular tissue of the archegonium, which is subjacent to it, but of that of the conical summit of the stem. In this manner it becomes firmly implanted, the tissue which surrounds it assuming the form of a sheath, and receiling the name of vagi nula. During this process, the dilated portion of the archegonium has increased in size, and has now attained about ten times its original length. Finally, it gives way at its line of junction with the vaginula, and is carried up wards on the summit of the still lengthening fruit.