BEYOPHYTA. 91 



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 scatter- 

 ing the spores after the sporogonium opens. 



Just before the spores are ripe, the stalk of the sporogo- 

 nium 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 (Ricciacece) 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 (Anthocerotece) , 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 (Marcliantiacece) includes the most con- 

 spicuous 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 differenti- 

 ated, 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 



