GROUP II. BRYOPHYTA : AID SGI. 



305 



The hypobasal half of the oospore undergoes but few divisions, forming a 

 bulbous foot, the superficial cells of which grow out into short papillaa. 



The fully developed sporogonium consists of a capsule attached to the foot by 

 a very short seta ; the wall of the capsule consists of a single layer of cells, and 

 has numerous stomata. The capsule opens by the throwing off of the apical 

 portion of the wall as an operculum. There is no peristome. 



When the calyptra is ruptured, it remains as a vaginula round the base of 

 the capsule. No part of it is carried upon the top of the capsule. 



The growth of the archegoniophore is stimulated by fertilisation. It grows 

 (Fig. 248 pa) out at its apex into a long, leafless stalk, the psendopodium, ex- 

 panded at the top into a cushion of cells in which the foot of the sporogonium 

 is embedded ; the perichaetial leaves grow and surround the base of tbe 

 stalk. 



The order consists of the single genus Sphagnum, of which there are many 

 species. 



Order II. Andreaeaceae. 



A. The GAMETOPHYTE. The germination of the spore and the various forms 

 of protonema are in many respects peculiar. Cell- divisions take place within 

 the spore before the rupture 

 of the outer coat (exospor- 

 ium), a plate of four cells, 

 sometimes a mass of a 

 larger number of cells, being 

 formed. By the expansion 

 of these cells the exospor- 

 ium is burst ; one or more 

 of the peripheral cells then 

 grow out into branched fila- 

 ments which grow apically, 

 segments being formed by 

 successive transverse walls ; 

 longitudinal walls are also 

 formed, so that the fila- 

 ments consist of two or more longitudinal rows of cells, and may develope into 

 flattened lobed plates of tissue. In some cases cell-divisions take place in 

 three dimensions, so that the protonema becomes cylindrical, consisting of four 

 rows of cells, and produces filamentous branches ; these cylindrical shoots be- 

 come erect, and present a shrubby appearance. Erect, flat, leaf-like plates of 

 tissue may be formed as lateral outgrowths on the protonema, resembling 

 similar structures in other Mosses [e.g. Tetraphis (Georgia) pellucida ; Tetrodon- 

 tium Brownianum]. All these forms of protonema, except the leaf-like struc- 

 tures, give rise to adult shoots as lateral buds. 



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

 main stem, closely covered with leaves, and is more or less branched. In an 

 old shoot the branch-system is a sympodium: the lateral branches are produced 

 laterally at the growing-point, and when, owing to the formation of reproduc- 

 tive organs at the apex, the growth of a main stem is arrested, they become 

 nearly erect and continue the growth of the shoot. Growth is apical, and is 



FIG. 249. A Plant of Ephemerum serratum, one of 

 the Bryineae ( x 20) : p protonema ; Ten bud ; b leaves ; 

 fc sporogonium j c calyptra. J5 Andrexa petrophila ( x 6): 

 ps pseudopodium ; fc capsule which has dehisced. 



