494 BOTANY PART n 



independent plants. Special branches of the tufted heads are distinguishable by 

 their different structure and colour ; on these the sexual organs are produced. 

 The male branches give rise, near the leaves, to spherical stalked antheridia. 

 The archegonia are borne at the tips of the female branches. The sporogonium 

 develops a short stalk with an expanded foot (B,C), but remains for a time enclosed 

 by the archegonial wall or calyptra. Upon the rupture of the archegonium, the 

 calyptra persists, as in the Hepaticae, at the base of the sporogonium. The 

 capsule is spherical and has a dome-shaped columella, which in turn is overarched 

 by a hemispherical spore-sac (spo) ; it opens by the removal of an operculum. 

 The ripe sporogonium is borne upon a prolongation of the stem axis, the pseudo- 

 podium, which is expanded at the top to receive the foot of the stalk. Of the 

 peculiar structure of the leaves and stem cortex a description has already been 

 given above. The protonema of the Sphagnaceae is in some respects peculiar. 

 Only a short filament is formed on the germination of the spore, the protonema 

 broadening out almost at once into a flat structure on which the young moss 

 plants arise. 



Order 2. Andreaeales 



The Andreaeales comprise only the one genus, Andreaea, small, brownish, 

 caespitose Mosses growing on rocks. The sporogonium is also terminal in this 

 order. The capsule, at first provided with a calyptra, splits into four longi- 

 tudinal valves (schizocarpous), which remain united at the base and apex 

 (Fig. 453). The "stalk is short, and is expanded at the base into a foot (Spf), 

 which in turn is borne, as in Sphagnum, on a pseudopodium (ps), a stalk-like 

 prolongation of the stem resulting from its elongation after the fertilisation 

 of the archegonium. The protonema is ribbon-shaped. 



Order 3. Bryales ( no ) 



In this order, which includes the great majority of all the true Mosses, the 

 moss fruit attains its most complicated structure. The ripe SPOROGONIUM, 

 developed from the fertilised egg, consists of a long stalk, the SETA (Fig. 454 s), 

 with a FOOT at its base, sunk in the tissue of the mother plant, and of a 

 CAPSULE, which in its young stages is surmounted by a hood or CALYPTIIA. 

 The calyptra is thrown off before the spores are ripe. It consists of one or two 

 layers of elongated cells, and originally formed part of the wall of the archegonium ; 

 this, at first, enclosed the embryo, growing in size as it grew, until, finally 

 ruptured by the elongation of the seta, it was carried up as a cap, covering the 

 capsule. It consists of several layers of cells and, especially in forms which occupy 

 dry habitats, bears hairs that correspond to protonemal threads of limited growth. 

 In some Mosses (e.g. Funaria) the young calyptra is distended and serves as a 

 reservoir of water for the young sporogonium ( in ). The upper part of the seta, 

 where it joins the capsule, is termed the APOPHYSIS. In Mnium (Fig. 460 A, ap) 

 it is scarcely distinguishable, but in Polytrichum commune it has the form of a 

 swollen ring-like protuberance (Fig. 454 ap\ while in species of Splachnum it dilates 

 into a large collar-like structure of a yellow or red colour. The upper part of the 

 capsule becomes converted into a lid or operculum which is sometimes drawn out 

 into a projecting tip. At the margin of the operculum a narrow zone of epidermal 

 cells termed the ring or ANNULUS becomes specially differentiated. The cells 

 of the annulus contain mucilage, and by their expansion at maturity assist in 

 throwing off the lid. In most Mosses the mouth of the dehisced capsule bears 



