156 MUSCINE^E 



All the species of the single genus Sphagnum (L.) grow in bogs and 

 swamps, often covering enormous tracts of ground, and entering largely 

 into the composition of peat. The best authorities differ widely as 

 to the number of species ; the most divergent forms are distinguished 

 by well-marked characters, but these merge into one another by a com- 

 plete series of connecting links. 



LITERATURE. 



Schimper Entwickelungsgeschichte der Torfmoose, 1858. 



Waldner Bot. Zeit., 1879, p. 595 ; and Entwickelung d. Sporogone v. Andreasa u. 



Sphagnum, 1887. 



Braithwaite Sphagnaceae of Europe and North America, 1880. 

 Warnstorf Die Europ. Torfmoose, 1881 ; and Flora, 1884. 

 Limpricht Bot. Centralbl., x., 1882, p. 214. 

 Roll Flora, 1886. 



Class VIII.-Hepaticas. 



The Hepaticae or Liverworts are small elegant plants, usually of a 

 bright green colour, which are especially abundant on damp ground or 

 rocks, or by the sides of streams ; a few species are aquatic. Some o'f 

 the genera bear a considerable external resemblance to lichens, others to 

 mosses. Their vegetative structure is either an undifferentiated thallus, 

 or consists of a distinctly differentiated stem and leaves, in both cases 

 attached to the soil by rhizoids. The former are known as the Thalloid 

 or Frondose, the latter as the Foliose Hepaticcz. The transition marks 

 the passage from the upper of the two great divisions of the vegetable 

 kingdom, the Cormophytes, to the lower division, or Thallophytes ; but 

 intermediate forms occur in the genera Fossombronia (Rad.) and Blasia 

 (Mich.). Even the foliose forms have no true vascular tissue, and no 

 true roots, the functions of which are performed by the rhizoids. Both 

 sections have, except in Riella (Mont.) and Haplomitrium (N. ab E.), a 

 distinct bilateral or dorsiventral structure ; the free side which faces the 

 light is differently organised from that which faces and often clings to the 

 substratum, and which is not exposed to light. The mode of branching 

 in the thalloid forms is dichotomous, and the growing region of the shoot 

 commonly lies in an apical depression formed by the more rapid growth 

 of the cells lying right and left of the apical cell, which has a form allied 

 to wedge-shaped. The filiform stem of the foliose forms, on the other 

 hand, ends in a bud with a more or less prominent cone of growth, 

 and the apical cell is a three-sided pyramid. The leaves of the foliose 

 forms always consist of only a single layer of cells, without even a rudi- 

 mentary midrib ; while the stem sometimes contains the first rudiments 



