1 88 SECOND GROUP. MUSCINEAE. 



An example will make this plain. Fig. 145 represents a portion of a longitudinal 

 section dividing the capsule of Funaria hygrometrica into two symmetrical halves ; e e 

 is the reddish -brown epidermis strongly thickened on the outside, and corresponds to a 

 in Fig. 142, C ; at the spot where the epidermis bulges out its cells have a peculiar 

 conformation and constitute the annulus ; se is the tissue between the epidermis of the 

 capsule and the air-cavity, the large-celled tissue/ is the continuation of the columella 

 inside the hollow of the operculum, s marks the uppermost cells of the archesporium. 

 The cell-layer which supplies the peristome rises immediately above the air-cavity h. 

 The outer walls of this layer a are much thickened and of a beautiful red colour, and the 

 thickening is continued for some way along the transverse walls ; the longitudinal walls 

 on the side towards the axis i are also coloured, but are less strongly thickened. Fig. 

 146 shows a part of a transverse section through the basal portion of the operculum ; rr 

 are the epidermal cells immediately under the annulus, which form the lower margin of 

 the operculum, a and i the thickened parts of the cell-layer concentric with the 

 operculum, which form the peristome. A section near the apex of the operculum would 

 show not the broad thickening masses i, /', /" but the middle portion of the inner wall, 

 only more strongly thickened. If we suppose then that when the capsule is mature the 

 annulus and operculum fall off, that the cells p and those between a and e (Fig. 145) 

 disappear, and that the unthickened portions of cell- wall between #, a\ a" and *, */ i" 

 in Fig. 146 are destroyed, the thick red portions of wall will be all that remains, and 

 these form sixteen pairs of tooth-like lobes pointed at the apex and rising in two 

 concentric circles above the margin of the capsule ; the outer lobes are the teeth, the 

 inner the cilia. The thickened cells at / in Fig. 145 connect the base of the teeth and the 

 margin of the capsule. The number of the teeth and cilia varies with the number of cells 

 in the layer that forms the peristome as seen in the transverse section, and according as 

 either one or two places are thickened in each of these cells, but it is always a multiple 

 of four, and usually sixteen or thirty-two. In many cases there is no thickening at / and 

 then the peristome is single and formed of the outer row of teeth only ; the thickening 

 at a is often much stronger than it is in Funaria^ and the teeth consequently are thicker. 

 The thickened portions of wall may also unite laterally with one another either wholly 

 or in part ; in that case the parts of the peristome form a membrane either above or 

 below, the teeth appear to be split above, and the endostome is composed of a lattice- 

 work of longitudinal or transverse bars instead of cilia (Fig. 143), or there is some similar 

 variation from the ordinary form ; the possible variations are many, but they are not 

 difficult to follow when the principle is clearly perceived. The inner and the outer faces 

 of the teeth of the peristome are hygroscopic ; hence as the moisture of the air varies 

 they curve inwards or outwards, or they twine round each other, as in Barbula. 



The Polytrichaceae, which include the largest and most highly developed Mosses, 

 differ in several points from the other groups in respect to the structure of their capsule. 

 The teeth of the peristome are not merely separate pieces of membrane but are formed 

 of bundles of thickened fibre-cells ; these bundles are in shape like a horse-shoe and are 

 placed with the horns of the crescent upwards, the horns of every two bundles uniting 

 to form one of thirty-two or sixty-four teeth. A layer of cells ep (Fig. 147) connects the 

 points of the teeth together and remains, when the operculum has fallen off and the 

 adjacent cells have dried up, as an epiphragm stretched across the mouth of the capsule. 

 The spore-sac in Polytrichumpiliferum and other species is separated from the columel a 

 by an air-cavity which, like the outer air-cavity, is traversed by conferva-like rows of cells. 

 The seta is in most species swollen beneath the capsule ; this enlargement of the seta, 

 which is known as the apophysis^ recurs in a somewhat different form in the genus 

 Splachnum, where it sometimes appears as a broad flat transverse disk. 



