GROUP II. BRYOPHYTA : MUSCI. 367 



thick-walled cells. The leaves have a prominent midrib ; the lamina consists 

 of a single layer of cells. 



B. The SPOROPHYTE. The first stages of the development resembles those 

 of Andreasa. The epibasal half of the embryo grows for a short time by means 

 of a two-sided apical cell. It undergoes differentiation, by the formation of 

 periclinal walls, into amphithecium and endothecium ; in the upper two-thirds, 

 of the capsule the innermost layer of the amphithecium becomes separated from 

 the outer layers, a large intercellular space being formed between them. 

 There is no arehesporial layer or columella, but isolated internal cells of the 

 endothecium are spore-mother-cells, each giving rise to four spores. The lower 

 part of the epibasal half forms the very short seta or neck. The hypobasal 

 half gives rise to a bulbous foot. There are uo stomata on the capsule. 



The ruptured calyptra surrounds the base of the sporogonium as a vaginula ; 

 no portion of it is raised up on the top of the capsule. The capsule ruptures 

 irregularly. 



The order includes the genus Archidium with the single species A. phascoides 

 (ulternifoliux.) 



OrderlV. Bryineae. 



A. The GAMETOPHYTE. The protonerna is filamentous, though in some 

 cases (e.g. Tetraphis pellucida and other Georgiaceag) it develops flattened 

 cellular appendages which are assimilatory organs {see AndreasaceaB, p. 365). 

 The subaerial portion of the protonema is generally short lived, though in some 

 cases it persists (e.g. Ephemerum) at least until the sporogonium has been 

 developed and the spores are ripe: the subterranean portion frequently persists 

 from year to year. The subaerial portion gives rise to the gametophores as 

 lateral buds; in some forms the subterranean portion produces lateral buds in the 

 form of bulbils (p. 355) which, when they are brought to the surface, give rise to 

 pametophores either directly or indirectly with the intetvention of protonema. 

 It is commonly the case that, when protonema is kept dry, some of the cells 

 grow larger and their walls thicker, whilst the other cells perish ; the persistent 

 cells, when moistened, developeinto filaments. 



The Adult Sfioot does not present, with regard either to its morphology or its 

 histology, am' especially characteristic features ; it varies in size from a mere 

 bud in such forms as Phascum and Ephemerum, where it is annual, to a shoot 

 several inches long in such forms as Fontinalis and Polytrichum where it is 

 perennial. In the latter case there is generally a central strand, and frequently 

 leaf-traces, in the stem. It may be either acrocarpous or pleurocarpous, a 

 feature which is important in the classification of the group. The leaves have 

 commonly a midrib : those of Leucobryum resemble those of Sphagnum in that 

 they consist of two kinds of cells, an internal layer of small living cells with chlo- 

 roplastids, and external layers of dead cells with perforated walls ; the peculiar 

 structure of the leaves of Polytrichum has been already described (p. 359). 



B. The SPOROPHYTE presents features, both as to its morphology and histo- 

 logy > which are characteristic of the group. It is differentiated into a true 

 hypobasal foot, a seta, and a capsule. The true foot is rudimentary. The 

 seta is relatively short in the lower forms : a false (epibasal) foot is fre- 

 quently developed from the lower portion of the seta. The neck of the capsule 

 has nearly always stomata in its epidermis, and is developed into a distinct 



