SECTION 17.] 



BRYOPHYTES. 



163 



to attach them to the soil, or to trunks, or to other bodies on which they 

 grow. Plants of this grade are chiefly Mosses. So as. a whole they take 

 the name of 



498. Bryopbyta, Bryophytes in English form, Bryum being the 

 Greek name of a Moss. These plants are of two principal kinds : true 

 Mosses (Musei, which is their Latin name in the plural) ; and Hepatic 

 Mosses, or Liverworts (Hepaticts). 



499. Mosses or Musoi. The pale Peat-mosses (species of Sphagnum, 

 the principal component of sphagnous bogs) and the strong-growing Hair- 

 cap Moss (Polytrichum) are among the lar- 

 ger and commoner representatives of this 

 numerous family ; while Fountain Moss (Fon- 

 tinalis) in running water sometimes attains the 

 length of a yard or more. On the other hand, 

 some are barely individually distinguishable 

 to the naked eye. Fig. 521' represents a com- 

 mon little Moss, enlarged to about twelve 

 times its natural size ; and by its side is part 

 of a leaf, much magnified, showing that it is 

 composed of cellular tissue (parenchyma-cells) 

 only. The leaves of Mosses are always sim- 

 ple, distinct, and sessile on the stem. The 

 fructification is an urn-shaped spore-case, in 

 this as in most cases raised on a slender stalk. 

 The spore-case loosely bears on its summit 

 a thin and pointed cap, like a candle-extin. 

 gnisher, called a Calyptra. Detaching this, it 

 is found that the spore-case is like a pyxis 

 (376), that is, the top at maturity comes off 

 as a lid {Operculum) ; and that the interior is 

 filled with a green powder, the spores, which 

 are discharged through the open mouth. In 

 most Mosses there is a fringe of one or two 

 rows of teeth or membrane around this mouth 

 or orifice, the Peristome. When moist the peristome closes hygrometri- 

 cally over the orifice more or less; when drier the teeth or processes 

 commonly bend outward or recurve; and then the spores more readily es- 

 cape. In Hair-cap Moss a membrane is stretched quite across the mouth, 

 like a drum-head, retaining the spores until this wears away. See Figures 

 527-541 for details. 



500. Fertilization in Mosses is by tne analogues of stamens and pistils, 

 which are hidden in the axils of leaves, or in the cluster of leaves at the 



Fia. 527. Single plant of Phyaoomitrium pyriforme, magnified. 528. Top of a 

 leaf, out across; it consists of a single layer of cell*. 



