June, 1922] 
DUPLER REBOULIA HEMISPHAERICA 
287 
is said to arise as a terminal lunate structure which becomes divided by 
the growth of the "apical branch" into two circular "secondary discs," 
these being pushed apart by the widening of the thallus between them and 
finally coming to occupy a marginal position. The writer has not found 
Figs. 1-12. Habit of the plant of Rehoulia hemisphaerica, showing the relation of 
female and male receptacles to one another and to the branching of the thallus. Male 
receptacles dotted. The dotted line indicates the midrib axis. Figure i shows a portion 
of the previous season's thallus with the base of the stalk of the old female receptacle. 
X 1.5. 
that the later growth of the thallus affects in any way the form of the 
receptacle, even the lunate disc not being at all correlated with the forking 
of the thallus (figs, i, 5, 9, 11). Both oval and lunate discs may occur on 
the same branch (fig. i), or two oval (fig. 2) or two lunate discs may succeed 
one another (fig. 11). 
Structure. The tissue of the young male disc is rather compact, but 
with the development of the antheridia the growth of the disc tissue exceeds 
that of the sex organs which thus become deeply imbedded in deep cham- 
bers opening to the exterior by narrow canals and simple air pores (fig. 16). 
Small air chambers develop between the canals. These chambers have simple 
pores, so far as found by both Haupt and the writer. Cavers (6) claims 
small barrel-type openings to occur occasionally. The disc is usually sur- 
