F. Cavers. 
166 
consists of two to four layers of cells, forming a cap which breaks 
into fragments when dehiscence occurs. The young carpocephalum 
is protected by two rings of scales; when the stalk elongates the 
inner scales are carried up on the receptacle, while the outer scales 
remain at the base of the stalk. 
In all the other genera of Operculatoe, the carpocephalum stalk 
has a rhizoid groove, and the development of a carpocephalum 
terminates the growth of the thallus. 
In Reboulia (Figs. 19-23), which is the only genus represented in 
Fig. 23. Reboulia hemispherica. A.—Part of Fig. 6, C., x 90, showing on the 
left the receptacle stalk with it ventral rhizoid-bearing groove, on the right 
one of the lobes (involucres) with a sporogonium enclosed in the calyptra. 
The outer portion of the lobe shows air-chambers, opening by large barrel¬ 
shaped pores, the inner portion consists of compact starch-bearing tissue. 
Between the stalk and the involucre are shown the narrow scales in cross- 
section. B.—Longitudinal section of a young sporogonium, with its calyptra. 
In the upper portion (capsule) of the sporogonium the archesporial tissue is 
shaded. x90. C.—-Upper portion of a nearly ripe capsule in longitudinal 
section, showing the lens-shaped apical cap and some of the spores and elaters. 
x 120. D.—Spore in surface view, from the inner side, showing the three 
radiating ridges. The surface is covered with a network of smaller ridges, 
x 200. E.—Spore in section, showing the thin endospore, the exospore (shaded), 
and the thick outer coat (epispore) with its ridges, x 200. 
