33 
Bryales. 
Fig. 71. — Dawsonia. I. Upper portion of capsule, with peristome of 
numerous bristle-like processes. II. Transverse section of upper portion of 
young capsule, showing the relatively broad peristome-forming zone. II. A 
portion of III, magnified to show the narrow thick-walled cells and the wide 
thin-walled cells of the peristome zone—the former produce the peristome 
teeth, the latter break down ; outside of the peristome zone is a layer of thin- 
walled tissue, which breaks down when the operculum becomes detached. 
IV and V. Diagrams showing the origin of the peristome processes (B) as 
small cells cut from the cells of the peristome zone, the remainder of each 
cell (A) being thin-walled and eventually breaking down. VI.- Part of a 
longitudinal section of young capsule, showing the narrow peristome cells (B) 
and the intermingled thin-walled cells (A). VII. A portion of a peristome 
tooth consisting of two rows of thick-walled cells. VIII. Longitudinal 
section of upper portion of nearly ripe capsule. IX. A portion of VIII, 
magnified highly. X. Detached operculum, cut longitudinally, to show the 
rod-like columella tissue which comes off with the outer cone-like tissue of the 
cap. A.s., air space; atm., annulus; col., columella; op., operculum; per., 
peristome; sp. s., spore sac. Except I., all the figures are from Goebel, but 
made somewhat diagrammatic. 
Fig. 72.— Polytrichum. I. Ripe capsule. II. Capsule after curvature 
of the seta and dehiscence of the operculum. Ill to VI, Diagrammatic tan¬ 
gential sections of the peristome-forming layer, showing the divisions which 
cut out the peristome-forming cells (B) from the thin-walled upper cell which 
becomes disorganised to form the pore between two adjacent peristome teeth. 
VII, three peristome teeth, each consisting of a bundle of cells. VIII, three 
cells isolated by maceration from a peristome tooth. Ill to VI and VIII 
from Goebel. 
