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 



Fig. 145. — Sphagnum sp. Photomicrograph of a longitudinal section 

 through a sporogonium and portion of the pseudopodium. op^ operculum; 

 r, annulus; ca, wall of capsule; 5/>, 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 



