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 ap?x. The amphi- 
thecial region of the apex develops in a 
259 
FIGS. 259, 260. True moss: 
259, longitudinal section of tip of 
p'ecuHar'way." The outer "-vails of onVof the y Ung s PJ> ro P^yte, showing differen- 
.... I, ,. x nation into amphithecium (three 
inner lavers of cells (usually the innermost) , , , . . , 
' layers of cells below) and endothe- 
become much thickened; this layer is an- dum . 26o> cross section of the same, 
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 cut, 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. 
The lower 
262 
Apophysis. 
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- P art f 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 5s then character- 
center) columella, single layer of sporogenous . , ,. 
cells, and eight or nine wall layers developed from lze(1 b 7 a S reater Display of 
the amphithecium. After CHAMBERLAIN. chlorophyll tissue and stomata 
