504 



ILLUSTRATIONS OF THE NATURAL ORDERS. 



lid, containing spores usually mixed with elaters (which are thin, 

 thread-like cells, containing one or two spiral fibres, uncoiling elas- 

 tically at maturity). Vegetation sometimes frondose, i. e. the stem 

 and leaves confluent into an expanded leaf-like mass ; sometimes 

 foliaceous, when the leaves are distinct from the stem, as in true 

 Mosses : the leaves are entire or cleft, two-ranked, and often with an 

 imperfect or rudimentary row (amphigastria) on the under side of the 

 stem. The matured pistillidium forms the sporangium or capsule, 

 which is either sessile or borne on a long cellular pedicel, and de- 

 hiscent by irregular openings, by teeth at its apex, or lengthwise by 

 two or four valves. The perianth is a tubular organ enclosing 

 the cah/ptra, which directly includes the pistillidium. Surrounding 

 the perianth are involucral leaves of particular forms. The an- 

 theridia in the foliaceous species are situated in the 'axils of peri- 

 gonial leaves. 



974. Subord. HicciaCCfl" consists of'a few chiefly floating plants, root- 

 ing from beneath, with their fructification immersed in the frond, the 

 sporangium bursting irregularly. No involucre nor elaters. — Ex. 

 Riccia. 



975. Subord. AnillOCCrctCeC. Terrestrial frondose annuals, with the 

 fruit protruded from the upper surface of the frond. Perianth none. 

 Sporangium pod-like, one- or two-valved, with a free central colu- 

 mella. Elaters none or imperfect. 



976. Subord. DlnrchailtiacCfP {True Liverworts). Frondose and ter- 

 restrial perennials, growing in wet places, with the fertile receptacle 

 raised on a peduncle, capitate or radiate, bearing pendent calyptrate 



FIO. 1314, 1315. Riccia natans, about the natural size 1316 Magnified section through 

 the thickness of the frond, showing the immersed sporangia ; one of which has burst through 

 and left an effete cavity. 1317. Magnified vertical section of one of the sporangia, with the 

 contained spores. 1318. Sporangium torn away from the base, and a quaternary group of 

 spores, united and separated. 



