II MUSCINE.-E— HEPATIC^— MARCHANTIACE^E 19 



very early are distinguished by their elongated shape from the 

 young spore mother cells. These elongated cells later develop 

 upon the inner surface of the cell wall peculiar spiral thickened 

 bands, which arc strongly hygroscopic. These peculiar fusiform 

 cells, the elaters, are found more or less developed in all tlic 

 Hepaticae except the lowest ones. The Anthoceroteae differ 

 very much from the other Hepaticae in the structure of the 

 sporogonium, as they do in other respects. Here alone among 

 Bryophytes the sporogonium may have unlimited growth, the 

 development continuing as long as the gametophyte remains 

 alive. While in the lowest genus, Notothylas, the growth is 

 limited, and the spores and elaters occupy the greater part of 

 the sporogonium, in AntJioceros the archesporium consists of 

 but a single layer of cells surrounding a central cylindrical mass 

 of tissue, the columella, and is separated from the outside of 

 the capsule by several layers of cells. The outer tissue is rich 

 in chlorophyll, and there is a well-developed epidermis with large 

 stomata differing neither in origin nor structure from those of 

 vascular plants. The foot is very large, and just above it is 

 a zone of actively dividing cells which cause the growth in 

 length of the sporogonium. 



The dehiscence of the sporogonium is different in the 

 different orders. In the Ricciaceee and some Marchantiaceae 

 the ripe sporogonium opens irregularly ; in a few cases (species 

 of Fimbriarid) the top of the capsule comes off as a lid ; in 

 most Jungermanniaceae the wall of the capsule splits vertically 

 into four valves, and in the Anthoceroteae the sporogonium 

 divides into two valves like a bean-pod. 



The spores are always of the tetrahedral type, i.e. the nucleus 

 of the spore mother cell divides twice before there is any 

 division of the cytoplasm, although this division may be 

 indicated by ridges projecting into the cell cavity, and partially 

 dividing it before any nuclear division takes plaice. The four 

 nuclei are arranged at equal distances from each other near the 

 periphery of the mother cell, and then between them are formed 

 simultaneously cell walls dividing the globular mother cell into 

 four equal cells having a nearly tetrahedral form. These 

 tetrads of spores remain together until nearly full grown, or in 

 a few cases until they are quite ripe. In the ripe spore two, 

 sometimes three, distinct coats can be seen, the inner one 

 (endospore, intine) of unchanged cellulose, the outer one 



