BRYOPHYTES 



119 



tissues between the epidermal layers dry up, and the spores are free in the large 

 cavity. 



Operculum and peristome. — The development of the operculum is complicated 

 (fig. 264). It is sometimes early differentiated from the capsule by a shallow de- 

 pression where a narrow zone of cells forms a 

 plane of cleavage. ' Above and below this 

 cleavage plane the tissue grows more rapidly, 

 resulting in two evident rings ; the upper one 

 is the annulus, the lower one the rim. The 

 rim is the more or less thickened top of the 

 urnlike capsule; but the annulus is a definite 

 ring which often becomes detached. The 

 sterile apex is at first solid, the center, occu- 

 pied by endothecial tissue, being a continua- 

 tion of the columella. The sporogenous 

 tissue and the region of cavities , end just 

 opposite the cleavage plane, so that they are 

 not represented at the apex. The amphi- 

 thecial region of the apex develops in a 

 peculiar way. The outer walls of one of the 

 inner layers of cells (usually the innermost) 

 become much thickened ; this layer is an- 

 chored to the rim below by a plate of thick- 

 walled cells. When the tissues of the capsule 

 dry out, all the tissues within the operculum. 



260 



Figs. 259, 260. — True moss: 

 259, longitudinal section of tip of 

 young sporophyte, showing differen- 

 tiation into amphithecium (three 

 layers of cells below) and endothe- 

 cium; 260, cross section of the same, 

 the cells of the endothecium shaded. 

 — After Chamberlain. 



Figs. 261, 262. — True moss: 261, longitudinal 

 section of tip of sporophyte showing (below) the 

 several wall layers (amphithecium), the sporoge- 

 nous layer (shaded) cut off from the endothe- 

 cium, and (above) the beginning of the operculum; always develop sporogenous 

 i62, cross-section of same, showing (beginning at tissue; it is then character- 



except this heavy layer of walls, 

 disappear, and the operculum 

 slips off like a cap, leaving these 

 heavy walls in a conical group of 

 toothlike projections (peristome) 

 anchored below to the rim. Some- 

 times there are two sets of peri- 

 stome teeth, in which case both 

 the inner and the outer walls of 

 the peristome-forming cells be- 

 come thickened. There are 

 many variations in peristomes 

 in detail of development and in 

 pattern. 



Apophysis. — The lower 

 part of the capsule does not 



center) columella, single layer of sporogenous 



the amphithecium. — After Ch.imberlain. chlorophyll tissueandstomata 



igie layer 01 sporogenous . , , j. t 1 c 



ceUs, and eight or nine wall layers developed from ^^ed by a__greater display of 



