ii MUSCINE&HEPA TIC IE MARCH A NTIALES 21 



Fam. i. Ricciacece 



Chlorophyll-bearing tissue with or without air-chambers, 

 and, where these are present, they never contain a special assim- 

 ilative tissue. Epidermal pores wanting or rudimentary. 

 Sexual organs immersed in open cavities upon the dorsal 

 surface. Sporogonium without foot or stalk, and remaining 

 permanently within the venter of the archegonium. All the 

 cells of the archesporium produce spores. 



Fam. 2. Corsiniacece. 



Air-chambers well developed; -epidermis with distinct 

 pores; sexual organs in distinct groups, but the receptacles 

 always sessile; sporogonium with a short stalk, producing 

 besides the spores sterile cells, which may have the form of 

 very simple elaters. 



Fam. 3. Marchantiacece 



Air-chambers usually highly developed, and the chambers 

 often containing a loose filamentous assimilative tissue. Pores 

 upon the dorsal surface always present (except in Dumortiera 

 and Monoclea) and highly developed, ring-shaped or cylin- 

 drical. Sexual organs always in groups, usually upon special 

 long-stalked receptacles. Sporophyte stalked and when ripe 

 breaking through the calyptra, opening by teeth or a circular 

 cleft, more seldom by four or eight valves. The archesporium 

 develops sterile cells, in the form of elaters, as well as spores. 



The Marchantiales constitute a very natural order of 

 plants, all of whose members agree very closely in their funda- 

 mental structure. The separation of the Ricciacese as a group 

 co-ordinate with the Jungermanniales and Marchantiales is not 

 warranted, as more recent investigations, especially those of 

 Leitgeb ( (7), vol. iv.) have shown that the two groups of the 

 Marchantiacese and Ricciacese merge almost insensibly into each 

 other. 



They are all of them strictly thallose forms, the thallus 

 being unusually thick and fleshy, and range in size from a few 

 millimetres in some of the smaller species of Riccia, to 10 to 20 

 centimetres in some of the larger species of Dumortiera and 

 Conocephalus. In most of them branching is prevailingly 



