BRYOPHYTA. 699 



long-stalked capsules inserted on its thallus — Metzgeria, branched and ribbon-like, 

 the curious aquatic Riella with its spiral membrane (see fig. 366, p. 611), and the 

 rather complex Symphyogyna and Pallavicinia (chiefly tropical), with their 

 creeping rhizomes and stalked fronds; these two forms, almost unique amongst the 

 Liverworts, show a well-marked vascular system. The antheridia and archegonia 

 are scattered over the surface of the thallus and not on stalked receptacles as in the 

 Marchantiacese. 



The leafy forms ai-e very numerous and, as a rule, consist of branched axes 

 which lie parallel to the substratum (e.g. FruUania dilatata, fig. 396 ^). There are 

 three rows of leaves, two towards the upper surface and one towards the lower. 

 These ventral leaves, which are termed amphigastria, are tiny and scale-like (see 

 fig. 396 ^), and sometimes are only represented by hairs. The archegonia are usually 

 borne in little groups at the tips of the main or lateral shoots, and are inclosed 

 in involucres. The antheridia occur in various positions. The sporogonium is 

 always a long-stalked capsule as in the thalloid forms. Not a few of the leafy 

 Jungermanniacese produce curious little appendages or "auricles'' at the bases 

 of their leaves, and these are often developed into little pitchers (fig. 396 '). In 

 other cases the amphigastria bear pitcher-like appendages of the same kind. These 

 structures seem to be receptacles for the holding of water by capillarity against 

 times of drought. In some forms Rotifers inhabit these pitchers (e.g. FruUania 

 dilatata, figs. 396 * and 396 ^), but there is no evidence to show that the Liverwort 

 uses their bodies as food like ordinary pitcher-plants, or that any special relations 

 exist between the Rotifers and the Liverwort. The pitchers are not gall-structures 

 directly produced by the Rotifer — they develop equally well with or without them. 

 They are probably formed by the plant simply for storing water, and are found by 

 Rotifers and other small animals to be convenient abiding-places. 



There are more than 3500 species of Jungermanniacese 



Alliance XXI. — Musci, Mosses. 



The oophyte generation is the leafy moss-plant; it arises as a lateral bud from 

 the simple and generally filamentous protonema. The sporogonium has a seta and 

 spore-capsule, the latter usually possessing a central sterile mass of tissue, the 

 columella. The upper portion of the archegonium is often raised as a calyptra by 

 the elongating sporogonium. 



Families: Sphagnacece, Andreceacece, Archidiacece, Bryacece. 



Sphagnacece. — These are the Bog-mosses, and they include a single genus. 

 Sphagnum. The form of the protonema here depends on whether the spore ger- 

 minates in water or upon a solid substratum; in the former case it is branched and 

 filamentous, in the latter it is a cellular expansion, not unlike a fern-prothallium. 

 The leafy moss-plant arises by budding from the protonema, and is remarkable on 

 account of its water-retaining properties. The character of the leaves has been 

 already described and figured at vol. i. p. 219. The sexual organs arise on special 



