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 (_Ricciaceæ_) 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 (_Anthoceroteæ_), 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 third order (_Marchantiaceæ_) includes the most conspicuous members of the whole class. Some of them, like the common liverwort (_Marchantia_), shown in Figure 57, _F_, _K_, and the giant liverwort (Fig. 57, _D_), are large and common forms, growing on the ground in shady places, the former being often found also in greenhouses. They are fastened to the ground by numerous fine, silky hairs, and the tissues are well differentiated, the upper surface of the plant having a well-marked epidermis, with peculiar breathing pores, large enough to be seen with the naked eye (Fig. 57, _E_, _J_, _K_) Each of these is situated in the centre of a little area (Fig. 57, _E_), and beneath it is a large air space, into which the chlorophyll-bearing cells (_cl._) of the plant project (_J_). The sexual organs are often produced in these forms upon special branches (_G_), or the antheridia may be sunk in discs on the upper side of the stem (_D_, _an._). [Illustration: FIG. 57.--Forms of liverworts. _A_, _Riccia_, natural size. _B_, _Anthoceros_ (horned liverwort), natural size. _sp._ sporogonia. _C_, _Lunularia_, natural size, _x_, buds. _D_, giant liverwort (_Conocephalus_), natural size. _an._ antheridial disc. _E_, small piece of the epidermis, showing the breathing pores, × 2. _F_, common liverwort (_Marchantia_), × 2. _x_, cups containing buds. _G_, archegonial branch of common liverwort, natural size. _H_, two young buds from the common liverwort, × 150. _I_, a full-grown bud, × 25. _J_, vertical section through the body of _Marchantia_, cutting through a breathing pore (_s_), × 50. _K_, surface view of a breathing pore, × 150. _L_, a leafy liverwort (_Jungermannia_). _sp._ sporogonium, × 2.] Some forms, like _Marchantia_ and _Lunularia_ (Fig. 57, _C_), produce little cups (_x_), circular in the first, semicircular in the second, in which special buds (_H_, _I_) are formed that fall off and produce new plants.