492 I'HE MOSS FAMILY. 



broken iu the middle, the lower portion remaining at the base of the 

 stalk, the other being carried up in the form of a conical cap, and 

 serving to protect the theca just as the calyx protects the young 

 corolla. The cap, technically called the " calyptra," is beautifully 

 exemplified in the common Polytrichum, where it is covered with 

 light-brown hairs, and hangs down with a ragged edge like Robinson 

 Crusoe's famous goat-skin cap. On the enlargement of the theca, or 

 at the period of ripeness, the calyptra generally splits up along one 

 side : it is then called " dimidiate." The calyptra being removed, the 

 theca is found to be closed at the mouth by a lid or " operculum " and 

 an intermediate coloured ring or " annulus," composed of large cellular 

 tissue, which by its expansion and contraction under the influence of 

 moisture and dryness, causes the lid to fall away as soon as the theca 

 is ripe. Then comes into view another and extremely beautiful part. 

 This is the "peristome," a single or double row of long fine teeth, 

 flattened at the base and tapering to a point, often of a delicate rose- 

 colour, and marked with transverse bars. The number of teeth varies 

 from four to eighty, but is always some multiple of four, as eight, 

 sixteen, thirty-two, sixty-four. At first they lie flat, or nearly so, the 

 points meeting in the centre, and thus forming a close cover to the 

 interior of the theca. Afterwards they rise up, and often bend back- 

 wards, like the white rays of a daisy, thereby enabling the spores to 

 escape. When damp they close again, and shut them in, presenting 

 all the phenomena of the opening and shutting petals of a sensitive 

 flower. In some mosses the stalk likewise is hygrometic ; in others 

 the peristome is absent ; in others, called Andrmi, the theca bursts 

 into four equal A^alves, the summits of which are held together by the 

 persistent operculum. Inside the theca is a central pillar called the 

 "columella," around which lie the innumerable spores. Sometimes 

 the antheridia and archegonia are on separate individuals, and the 

 plants are then said to be dioecious. Nothing is known from actual 

 observation of the functions of the former, but it is a well established 

 fact that wherever they are absent, thecaj are not produced from the 

 archegonia. Some authors consider the theca of mosses, with its 

 various parts, as analogous to the entire blossom of a flowering plant 

 rather than to the ripened ovary or seed-vessel, which it appears to 

 those Avho consider the antherid'a as analogues of stamens. 



The number of known mosses is considerable, and a multitude no 

 doubt remain undiscovered, since they grow in every part of the world. 

 The species enumerated as natives in Wilson's "■' Bnjologia" (1855) 



