Marchantiacece. 
169 
thallus being surrounded by concentric rings of cells. In Exor- 
motheca the roof of each chamber grows up to form a long chimney¬ 
like projection with the pore on its summit; this is merely an 
exaggeration of the convex form of roof seen in Fegatella (Figs. 24, 
25). 
Fig. 24. Fegatella conica. Transverse section through midrib of thallus 
showing the upper zone of air-chambers and the lower zone of compact tissue, 
with four of the mucilage sacs. Sm. rh., smooth-walled rhizoids ; tub. rh., 
tuberculate rhizoids ; v.s., ventral scales, x 30. 
Fig 25 Fegatella conica. Part of a vertical section of the thallus, showing 
an air-chamber, lined by pointed cells and opening above by a pore in the 
epidermis, x 180. 
In this group the Marchantiaceous thallus reaches its greatest 
complexity. The compact tissue underlying the air-chamber layer 
contains large oil-bodies, filling up certain cells; mucilage sacs, 
either isolated, or arranged in groups ( Exormotheca ), or in longitu¬ 
dinal rows ( Fegatella ); sclerotic fibres (Preissia— Fig. 27—and some 
species of Marchantia) ; and a mycorhiza (Preissia, Fegatella). The 
ventral scales are generally well developed (except in Duinortiera, 
where they are rudimentary, as might be expected from the hygro- 
philous habitat), and have an apical appendage separated from the 
