366 PART III. THE CLASSIFICATION OF PLANTS. 



effected by means of a three-sided apical cell. The leaves are sessile, the lower 

 leaves are small and deciduous. 



The Sexuil Organs are borne in terminal groups on the shoots ; the male and 

 female organs are always borne on distinct branches, generally on the same plant 

 (monoacious) , or on distinct plants (dioecious) : since, in both cases, the apical 

 cell of the shoot gives rise to a sexual organ, the growth of the shoot is arrested 

 by the development of the reproductive organs. The group of sexual organs 

 is surrounded by involucral leaves, and amongst them are developed filamentous 

 paraphyses. The antheridia have short stalks : the archegonia have short stalks 

 and very long necks. 



The Structure of the Adult Shoot is simple ; there is no central strand ; the 

 peripheral cells are narrower than the internal cells, and their walls are of a 

 yellowish colour. 



The leaves consist of a single layer of cells all containing chloroplastids : in 

 some species there is a midrib consisting of several layers of cells. 



B. The SPOBOPHYTE. A two-sided lenticular apical cell is formed, in the 

 epibasal cell, by two oblique intersecting walls, from the two sides of which 

 about twelve segments are alternately cut off. In the upper segments cut off 

 from the apical cell the amphithecium and the endotheciurn are differentiated ; 

 the two lower segments (on each side) form the short seta of the sporogonium. 

 The hypobasal .cell undergoes a few divisions to form the foot. 



The archesporium is differentiated from the external layer of the endothe- 

 ciurn, the rest of the endotheciurn forming the columella. The archesporium 

 has the form of a hollow cone, covering the top of the columella ; no intercel- 

 lular spaces are formed. 



When the calyptra is ruptured, the upper portion is borne on the top of the 

 capsule as a cap ; the lower, the vaginula, invests the short seta. The capsule 

 dehisces by four longitudinal fissures, extending to neither the base nor the apex 

 (Fig. 249 B) : there is no operculum, or peristome, nor has the wall of the 

 capsule any stomata. 



The shoot is stimulated to growth, after fertilisation, producing a short leaf- 

 less pseudopodium, which carries up with it the unfertilised archegonia of the 

 group : the perichastial leaves also develope, and invest the base of the pseudo- 

 podium. 



The Andreseaceffi are small caespitose Mosses (Fig. 250 ft) growing on rocks in 

 mountainous districts. The order consists of the single genus Andreaea. 



Order III. Archidiaceae. 



A. The GAMETOPHYTE. Theprotonema is filamentous, and the subterranean 

 portions of it are perennial : it gives rise to numerous adult shoots. 



The Morphology of the Adult Shoot. The adult shoot consists of a very short 

 stem with"scattered leaves. It bears lateral branches, both sterile and fertile ; 

 the former are long and decumbent, and give rise in the succeeding year to 

 erect fertile shoots. The male and female organs are either borne, together 

 with paraphyses, terminally on distinct branches of the same plant ; or the 

 antheridia are borne singly in the axils of the perichaetial leaves of the female 

 receptacle. 



The Structure of the Adult Shoot. There is a central strand of conducting 

 tissue, surrounded by parenchymatous cells ; externally is a layer of narrow 



