HEPATICAE. 501 



dependent individual, the very different sporophyte partially or 

 wholly parasitic on the gametophyte. Gametophyte dorsiventral, 

 consisting of a thallus or more or less differentiated into stem and 

 leaves, attached to the substratum by means of rhizoids (true roots 

 none), growing by means of an apical cell. Sexual organs borne on 

 the upper surface of the gametophyte or terminal on more or less 

 differentiated branches. Fertilized egg developing directly into the 

 sporophyte, the wall of the venter of the archegonium usually de- 

 veloping into a protective cover, or calyptra, which is not ruptured 

 until the sporophj^te is nearly mature. Sporophyte consisting of a 

 capsule only or differentiated into a capsule (spore-bearing organ), 

 a stalk or a growing region, and a foot (absorbing organ). Capsule 

 consisting of a wall of sterile cells and a spore-sac, the latter some- 

 times with a median sterile portion (columella), dehiscing irregu- 

 larly or by means of a lid or of longitudinal splits ; spore-sac con- 

 taining spores onl}^ or spores and elaters, the latter consisting of 

 sterile cells, often elongated and usually developing spiral bands of 

 thickening on their walls. 



Gametophyte a thallus or leafy shoot. Chloroplasts minute, many in each cell. 

 Capsule short, spherical to oval, without a columella, borne on a translucent 

 stalk. 

 Gametophyte a thick and fleshy thallus. usually pale and differentiated into dis- 

 tinct tissues, rarely deep green and succulent ; green tissue usually with air- 

 spaces. Capsule splitting irregularly or by 



means of a lid. Order 1. Marchantiales. 



Gametophyte a delicate thallus or a leafy shoot ; 

 tissue differentiation slight : air-spaces not pres- 

 ent. Capsule splitting into four longitudinal 



valves. Order 2. Juxgermanniales. 



Gametophyte a thick and fleshy thallus, dark green 

 and succulent, tissue differentiation slight. Chloro- 

 plasts large, usually borne singly. Capsule long, 

 cylindrical, with a basal growing region, splitting 

 into two longitudinal valves. Order 3. Axthocerotales. 



Order 1. MARCHANTIALES. 



Gametophyte a prostrate, strap-shaped, dorsiventral thallus, growing 

 apically, branching diehotomonsly or from the ventral surface of the 

 median portion, and showing a distinct differentiation into tissues, the green 

 tissue usually with air-spaces. Ventral scales more or less distinct. Rhi- 

 zoids of two kinds, the one with smooth walls, the other with interior peg- 

 like papillae. Antheridia in deep depressions on the upper surface of the 

 thallus, sometimes scattered, sometimes grouped together in more or less 

 definite, sessile or stalked receptacles. Archegonia similar in position but, 

 when borne on stalked receptacles (carpocephala), becoming displaced to 

 the lower surface through intercalary growth. Sporophyte a capsule only 

 or differentiated into capsule, stalk, and foot; elaters (or other sterile 

 cells) usually present in the capsule. 



Sporophyte consisting of a capsule only. Fam. 1. Ricciaceae. 



Sporophyte differentiated into capsule, stalk and foot. Fam. 2. Marchantiaceae. 



