68. Archegonia.— The rudiments of the ar chegonia make their appearance as oval cellular bodies (from low- to twelve in number) in the notch, which in Pellia, as in other fron dose Hepaticx, is found in the anterior margin of the young shoot. Soon after 'their origin, there is formed, by the continued growth of the shoot below them, a thin laminar prolong ation upon the surface of which they are sup ported. By a process of cell-division resem bling that observed in the development of the antheridia of Anthoceros, each rudiment is converted into a cylinder, rounded above and consisting of a single central cellular column, surrounded by a single layer, which is formed of four perpendicular series of flattened cells in contact with each other by their edges. The cells of the central column contain granular mucus, in which ve sicular nuclei are embedded. As the arche gonium becomes fully formed, the lowest cell in the series, as well as its nucleus, enlarges, and the cells of the outer wall in its neigh bourhood rapidly multiply, so that the organ becomes swollen out at its lower part. The development is completed by the disappearance of the transverse septa, which separate the cavities of the cells forming the central column. In this manner is produced an axile channel, closed above, and terminating below in a flask-shaped dilatation, in which the enlarged nucleus of the basal cell cell) is contained. Soon the cells forming the summit of the archegonium give way, so as to open a communication between its cavity and the external atmosphere.
69. Second period.—Development of the enz bryo.—In consequence, as there is every reason to believe, of the entrance of the spiral filaments into the cavity of the archegonium. the germ cell is divided by a tranverse septum into a larger inferior and smaller superior (hemi spherical) portion. This last next divides by two perpendicular septa crossing each other at right angles, which are succeeded by a third, which is horizontal. This is succeeded by others parallel to it, each new septum being placed immediately above its predecessor. Hence results a cellular cylinder, the rounded summit of which always consists of four cells, divided from each other by crucial septa. By successive cell-divisions, this body becomes a pear-shaped cellular mass. Afterward by the lengthening of its middle third, the cylindrical stalk of the perfect fruit is formed, and still later from the lower third springs a cup shaped sheath, the margin of which reaches to about a third of the length attained by the stalk of the fruit before it has escaped from its calyptra.
70. Changes preparatory to the development of the spores.—At an early period, when the young fruit is still pear-shaped, its rounded up per end (the future capsule) manifests peculi arities in its intimate structure. The cells of its superficial layer are divided repeatedly by septa perpendicular to the surface, while those which they enclose graaually enlarge without dividing. The result of this process is the formation of a central mass of large dodecahe dral cells (parent cells of the spores and elaters), which is surrounded by a single layer of tabular cells of not more than a quarter their breadth (the future wall of the capsule).
As the development proceeds, the walls of the central cells become thickened by the deposit of a gelatinous material on their internal sur faces. This material, which is coloured violet by iodine, swells out, and finally dissolves, on the addition of water, the globular primordial vesicle, which occupies the centre of the cells, being brought into view. Still later both the cell membranes and their gelatinous linings disappear, and the primordial membranes are left, lying in the cavity of the young capsule. Soon after they clothe themselves with new membranes of cellulose, and assume forms, which differ according as they are destined to become parent cells of spores or elaters. Those of the newly formed cells which are to be elaters, assume the form of spindles. They are found partly grouped round the axis of the capsule, partly in series which radiate from it towards the circumference. The future parent cells retain only for a short time their globular contour : soon four projections of the mem brane of each cell become visible, each of which would correspond in position to one of the angles of a regular tetrahedron contained in the parent cell. These projections increase so rapidly, that in a short time the whole presents the appearance of four egg-shaped sacculi blended together by their smaller ends in such a manner that their axes meet at a central point, each forming with all the rest angles of 120°. The cell-wall now becomes thickened by the deposition of a granular material on its inner surface, which takes place most rapidly along the linear ridges which separate the sacculi. En this manner six imperfect dissepirnents are formed, which stretch from the ridges towards the centre, and encroach so far on 'the central cavity, that it now communicates with the cavities of the sacculi only by four narrow circular channels. These changes are followed by the formation in each sacculus of a delicate vesicle (the spore) completely filling the cavity of each. No sooner has this taken place than those por tions of the parent cell which correspond to the sacculi dissolve and disappear, the four oval spores remaining attached for several days to the still permanent tetrahedral cen tral portion, which consists of vitreous cellu lose. The central nucleus of each spore now disappears, and is replaced by two others, around which the mucous aud chlorophylle granules group themselves. A septurn is soon after forrned between them, dividing the spore into two halves, in each of which the process is repeated. In the meantime the coloured external membrane is secreted on its external surface. The ripening of the capsule and consequent scattering of the spores takes place in spring, a year after the development of the archegonium within which the fruit originated.