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t division wall to be formed in the embryo is transverse, and is followed by vertical ones (Fig. 54, _E_, _em._). As the embryo enlarges, the walls of the basal part of the archegonium grow rapidly, so that the embryo remains enclosed in the archegonium until it is nearly full-grown (Fig. 55). As it increases in size, it becomes differentiated into three parts: a wedge-shaped base or "foot" penetrating downward into the upper part of the plant, and serving to supply the embryo with nourishment; second, a stalk supporting the third part, the capsule or spore-bearing portion of the fruit. The capsule is further differentiated into a wall, which later becomes dark colored, and a central cavity, in which are developed special cells, some of which by further division into four parts produce the spores, while the others, elongating enormously, give rise to special cells, called elaters (Fig. 56, _B_). [Illustration: FIG. 56.--Spore (_A_) and two elaters (_B_) of _Madotheca_, x 300.] The ripe spores are nearly globular, contain chlorophyll and drops of oil, and the outer wall is brown and covered with fine points (Fig. 56, _A_). The elaters are long-pointed cells, having on the inner surface of the wall a single or double dark brown spiral band. These bands are susceptible to changes in moisture, and by their movements probably assist in scattering the spores after the sporogonium opens. Just before the spores are ripe, the stalk of the sporogonium elongates rapidly, carrying up the capsule, which breaks through the archegonium wall, and finally splits into four valves, and discharges the spores. There are four orders of the liverworts represented in the United States, three of which differ from the one we have studied in being flattened plants, without distinct stems and leaves,--at least, the leaves when present are reduced to little scales upon the lower surface. The first order (_Ricciaceae_) are small aquatic forms, or grow on damp ground or rotten logs. They are not common forms, and not likely to be encountered by the student. One of the floating species is shown in figure 57, _A_. The second order, the horned liverworts (_Anthoceroteae_), are sometimes to be met with in late summer and autumn, forms growing mostly on damp ground, and at once recognizable by their long-pointed sporogonia, which open when ripe by two valves, like a bean pod (Fig. 57, _B_). The thi
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