CRYPTOGAMS 



389 



surmounted by a narrow layer of sporogenous cells. Elaters also occur ; they are 

 multicellular, variously shaped, and often forked. The sporogonia, unlike those of 

 all other Hepaiicae, do not ripen simultaneously throughout their whole length, but 

 from the tips downwards, and continue to elongate by 

 basal growth after emerging from the archegonia. 



On the under side of the thallns, fissure-like openings, 

 formed by the separation of the cells, lead into cavities 

 filled with mucilage. Nostoc filaments penetrate into 

 these cavities, and develop into endophytic colonies. 



Fig. 



318. — Anthoceros laevis. 

 sp, Sporogonium ; c, colu- 

 mella. (Nat. size.) 



Order 4. Jungermanniaeeae 



In the simplest forms of this order the thallus is 

 broadly lobed, similar to that of Marchantia {e.g. Pellia 

 cpiphylla, frequently found on damp ground) ; or, like 

 that of Riccia fluitans, it is narrow and ribbon-shaped, 

 and at the same time profusely branched (e.g. Metzgeria 

 furcata, Fig. 161, p. 149). In other forms, again, the 



broad, deeply-lobed thallus has an evident midrib, and its margins, as in the case of 

 Blasia pusilla (Fig. 11, p. 14), exhibit an incipient segmentation into leaf-like 

 members. The majority of Jungermanniaceae, however, show a distinct segment- 

 ation into stem and leaflets. The latter consist of one layer of cells without a 

 midrib, and are inserted with obliquely directed laminse in two rows on each flank 

 of the stem. Some species (e.g. Frullania Tarnarisci, a delicately branched 

 Liverwort of a brownish colour occurring on rocks and tree -trunks) have also 

 a ventral row of small scale - like leaves, amphigastria (Fig. 319, a). The dorsal 



leaves are frequently divided into an upper and 

 lower lobe. In species growing in dry places, like 

 the previously cited Frullania, the lower lobe is 

 modified into a sac, and serves as a capillary water- 

 reservoir. The leaves regularly overlap each other ; 

 they are then said to be succubous, when the pos- 

 terior edges of the leaves are overlapped by the 

 anterior edges of those next below (Frullania, Fig. 

 319), or incnbous, if the posterior edges of the 

 leaves overlap the anterior edges of the leaves next 

 above (PlagiocMla, Fig. 12, p. 14). 



The branching stems of the foliose Jungerman- 

 niaceae are either prostrate or partially erect, and 

 in consequence of the manner in which the leaves 

 develop, present a distinctly dorsiventral appearance. 

 The long-stalked sporogonium is also charac- 

 teristic of this order ; it is already fully developed 

 before it is pushed through the apex of the arche- 

 gonial wall by the elongating stalk. It has a 

 spherical capsule which on rupturing splits into four valves (Figs. 11, 12). No 

 columella is formed in the capsule ; but in addition to spores it always produces 

 elaters, which by their movements while drying scatter the spores. 



According to the position of the sporogonia, two sub-orders are distinguished. 

 (a) Anacrogynous Jungermanniaceae. — The sporogonia arise laterally, and are 

 situated on the dorsal side of the thallus or stem. They are encircled at the base 



Fia. 319.— Part of a shoot of Frul- 

 lania Tarnarisci, seen from below. 

 r, Dorsal leaves with the lower 

 lobes (ws) modified as water-sacs ; 

 a, anipliigastrium. (x 36.) 



