158 AfOSSES AND FERNS chap. 



at least in California. Other Mosses are perennial, and some 

 species of peat or tufa-forming Mosses seem to have an unlimited 

 growth, the lower portions dying and the apices growing on 

 until layers of peat or tufa of great thickness result, covered 

 over with the still living plants whose apices are the direct 

 continuation of the stems which form the basis of the mass. 



With the exception of a very few forms all the Mosses are 

 readily referable to three orders. The first two, the Sphagnacese 

 and the Andreaeaceae, are represented each by a single genus, 

 and are in several respects the forms that come nearest the 

 Liverworts. All the other Mosses, except perhaps ArcJiidium 

 and Buxbaumia, conform to a very well - marked type of 

 development, and may be referred to a common order, the 

 Bryineae. The Phascacea^ or cleistocarpous forms are sometimes 

 separated from the higher Bryineae as a distinct order, but a 

 study of their development shows that they belong to the same 

 series, and only differ in the degree of development from the 

 more specialised stegocarpous forms. 



Order I. Sphagnacem 



The Sphagnaceae, or Peat-Mosses, are represented by the 

 single genus Sphagnum. They are Mosses of large size, which, 

 as is well known, often cover large tracts of swampy land and 

 about the borders of lakes, forming the familiar peat-bogs of 

 northern countries. Owing to the empty cells in the leaves and 

 outer layers of the stem, they suck up water like a sponge, and 

 the plants when growing are completely saturated with water. 

 The colour is usually pale green, but varies much in depth of 

 colour, and in many species is red or yellow. When dry the 

 colour is much duller, largely owing to the opacity of the dry, 

 empty cells which conceal to a great extent the colour of the 

 underlying tissues. They branch extensively, and, according to 

 Schimper, a branch is always formed corresponding to every 

 fourth leaf ; but Leitgeb has shown that although this is the 

 rule numerous exceptions to it occur. In sterile plants the 

 branches are of two kinds, long flagellate branches which hang 

 down almost vertically and are applied to the stem, and much 

 shorter ones that are crowded together at the apex and have 

 only a limited growth. The leaves are inserted on the stem 

 by a broad base, and taper to a more or less well-marked point. 



