BRYOPHYTES 



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

 cavity. 



Opetculumand 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- 



259 



FIGS. 259, 260. True 



tiation into amphithecium (three 

 layers of cells below) and endothe- 

 260, cross section of the same, 



thecial region of the apex develops in a 2 59> longitudinal section of tip of 

 peculiar way. The outer walls of one of the g phyte ' owing dif&ren- 

 inner layers of cells (usually the innermost) 

 become much thickened; this layer is an- 



^*v*i.ii, *v\J, V.HJ33 3C<_llUll UJL 111C SitlllC, 



chored to the rim below by a plate of thick- the cells of the endothecium shaded. 



walled cells. When the tissues of the capsule After CHAMBERLAIN. 



dry out, all the tissues within the operculum, 



except this heavy layer of walls, 

 disappear, and the operculum 

 slips off like a cap, leaving these 

 heavy walls in a conical group of 

 tooth like 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. 



lower 



262 



Apophysis. The 



FIGS. 261, 262. True moss: 261, longitudinal 

 section of tip of sporophyte showing (below) the 

 several wall layers (amphithecium), the sporoge- r , 

 nous layer (shaded) cut off from the endothe- P art ot the ca psule does not 

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

 262, cross-section of same, showing (beginning at tissue; it IS then character- 

 center) columella, single layer of sporogenous .'.. j- i 

 cells, and eight or nine wall layers developed from lzed b 7 a greater display of 

 the amphithecium. After CHAMBERLAIN. chlorophyll tissue and Stomata 



