450 



MARCHANTIACEAE. 



receptacles discoid, sessile or stalked; carpocephala discoid, invariably 

 stalked, the stalk sometimes with one or two rhizoid-furrows. Sporophyte 

 differentiated into a capsule, stalk and foot, the capsule forced through the 

 eah^ptra at maturity by the elongating stalk and dehiscing irregularly or 

 by means of a more or less distinct lid; elaters present in the capsule. 

 Gemmae discoid, present in two genera. About 25 genera and 200 species, 

 widely distributed, especially in warm regions. 



Air-chambers and epidermal pores (visible with a lens) present. 



Boundaries of air-chambers indistinct ; gemmae never present. 1. RebouUa. 

 Boundaries of air-chambers distinct ; gemmae usually present. 



Gemmae in crescentic conceptacles. 2. Lnniilaria. 



Gemmae in circular conceptacles. 4. Marchantia. 



Air-chambers and epidermal pores not present. 3. Dumortiera. 



1. REBOULIA Eaddi. 

 Thallus branching dichotomously or innovating at the apex and thus 

 appearing jointed. Air-chambers with indistinct boundaries, arranged in 

 several layers and separated from one another by plates of green cells with 

 occasional perforations; epidermal pores bounded by several concentric rows 

 of cells in a single layer, arranged in distinct radiating series, not opening 

 into all the air-chambers. Ventral scales pigmented, divided into a basal 

 portion and one to three appendages. Antheridial receptacle oval to semi- 

 lunar, sessile, surrounded by a deep groove and by a series of narrow scales. 

 Carpocephalum arising from the extremity of a thallus-branch, hemispherical 

 and bluntly lobed, the long stalk with a single rhizoid-furrow; arehegonia five 

 to eight (mostly six or seven), arranged peripherally under the lobes; in- 

 volucre (around each archegonium or young sporophyte) consisting of two 

 overlapping longitudinal folds with entire margins; pseudoperianth none. 

 Capsule with a very rudimentary lid; cells of wall destitute of ring-like thick- 

 enings. [Commemorates Eugene de Eeboul, a French botanist.] A mono- 



typic genus. -^^ /rx 



/.;*.>. /^« 2 Reboulia hemisphaerica (L.) 



Raddi. Eeboulia. (Fig. 495.) Thallus 

 pale green, varying to purple, about 5" 

 wide and l'-2' long, more or less crispate 

 along the margin. Appendages of ven- 

 tral scales usually two, narrowly lanceo- 

 late, composed of elongated cells; in- 

 florescence dioecious or monoecious; 

 antheridial receptacle terminal on a thal- 

 lus-branch or, in monoecious plants, some- 

 times borne immediately behind a female 

 receptacle; spores yellow at maturity, 

 about 60 fi in diameter, the surface loosely 

 and irregularly reticulate and finely ver- 

 ruculose ; elaters usually with two yellow 

 bands of thickening. [Marchantia hemi- 

 sphaerica L.] 



On stone walls and along roadsides. 

 The commonest thalloid liverwort on the 

 island ; almost cosmopolitan in its distri- 

 bution. 



