MUS01NBJB. 



191 



surface of the thallus is divided into small rhombic areas, in the 

 centre of each of which is found a large, peculiarly constructed 

 stoma (Fig. 197 A) ; beneath each of these a large air-cavity is to 

 be found. From the floor of the air-cavity a number of alga- 

 like cells project into it; these contain chlorophyll and are 

 therefore the assimilating cells. The antheridia and archegonia 

 are each found aggregated on specially formed branches (some- 

 what resembling Mushrooms) projecting from the surface of the 

 thallus. The antheridia are developed on the upper surface (Fig. 

 197 C, D) and the archegonia on the lower (Fig. 197 A, B), near 

 the centrally-placed stalk. 



Marchanticu polymorpha is dioecious (Fig. 197), and very common 

 on damp places. Lunularia (South Europe), frequently found 

 on flower-pots in conservatories ; Preissia, Fegatella, Rebotilia, 

 Targionia. 



Family 2. Anthoceroteae. 



These have an entirely leafless, fleshy, flat, and irregularly-shaped thallus. 

 In its intercellular chambers Nostoc-colonies are often found, which have forced 

 their way through the stomata situated on the under side. The antheridia and 

 archegdhia arise from the cells lying inside the thallus. The capsule resembles 

 a long, thin pod; it has two valves and a columella. Anthoceros (A. lcevis t 

 Fig. 194, and punctatus) . 



Family 3. Jungermannieae. 



Some forms in this family have a thallus in which leaf -like 

 structures are found (Blasia), while in 

 others (e.g. Metzgeria, Pellia, Aneura) they 

 are entirely absent. The majority, how- 

 ever, have round, thick stems, bearing 

 dorsally two rows of leaves, and one row 

 ventrally. Some of these have the leaves 

 " underlying " (Fig. 195), while in others 

 (Fig. 198) they are " overlying." (See Figs. 

 195, 198, with explanation). 



The sporangia are spherical, stalked, and 

 situated singly on the apex of the branches, 

 and open by four valves (in Sphcerocarpus 

 they are indehiscent). 



All the species in this family were 

 formerly reckoned as belonging to one 

 genus, Jungermannia, but now they are 

 divided into several, arranged as follows : 



\v. B. 



FIG. 198. Frullania dila. 

 tata. Portion of a branch 

 seen from the under side : 

 r and b are the anterior and 

 posterior edges of the same 

 dorsal leaf; a ventral leaves 

 (amphigastria). The dorsal 

 leaves are " overlying," i.e. 

 the anterior edge of the 

 leaf overlaps the posterior 

 edge of the preceding one. 

 O 



