200 
STRUCTURE AND LIFE HISTORIES 
of the developing embryo become organized into a large 
globular spore-case, containing a thick central column 
(columella), surrounded by a dome of spores, and, out- 
side of all, the wall of the sporangium. As the spore-case 
.-_ ps 
FIG. 145. Sphagnum sj>. Photomicrograph of a longitudinal section 
through a sporogonium and portion of the pseudopodium. op, operculum; 
r, annulus; ca, wall of capsule; sp, spores; col, columella; /, foot; ps, pseu- 
dopodium. 
enlarges the wall of the archegonium is ruptured and the 
top portion of it is carried up as a cap on the spore-case, 
forming the calyptra. The lower cells produced by the 
dividing oosperm become organized into a much swollen 
