436 BOTANY PART n 



spore-sac (spo) ; it possesses an operculum, but no peristome. The ripe sporogoniuin, 

 like that of Andreaea, 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. Andreaeaeeae 



The Andreaeaeeae 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 longitudinal 

 valves (schizocarpous), which remain united at the base and apex (Fig. 390). The 

 stalk is short, and is expanded at the base into a foot (Spf), which in turn is 

 borne on a pseudopodium (ps), a stalk-like prolongation of the stem resulting from 

 its elongation after the fertilisation of the archegonium. 



Order 3. Phascaceae 



To the Phascaceae (Cleistocarpae) belong small Mosses with few leaves growing 

 on the soil ; they retain their filamentous protonemata until the capsules are ripe, 

 and have the simplest structure of all the Mosses (Fig. 391). The capsule is 

 terminal and has only a short stalk ; it is protected by a calyptra. It does not 

 open with a lid, but the spores are set free by the decay of its walls. 



Order 4. Bryinae( 105 ) 



In this order (termed also Stegocarpae), which includes the 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. 392 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 CALYPTRA. 

 The calyptra is thrown otf 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 

 which, 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. In the Liverworts the calyptra is, on the contrary, always pierced by 

 the elongating sporogonium, and forms a sheath at its base. The upper part of 

 the seta, where it joins the capsule, is termed the APOPHYSIS. In Alnium (Fig. 

 398 A, ap) it is scarcely distinguishable, but in Polytrichum commune it has tin: 

 form of a swollen ring-like protuberance (Fig. 392, 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 ANNTLUS becomes specially 

 differentiated. The cells of the aunulus contain mucilage, and by their expansion 

 at maturity assist in throwing off the lid. In most stegocarpous Mosses the 

 mouth of the dehisced capsule bears a fringe, the PEKISTOME, consisting usually 

 of tooth-like appendages. 



