290 
AMERICAN JOURNAL OF BOTANY 
[Vol. 9, 
mology which exists between the male and female receptacles throughout 
the Marchantiaceae." 
Sexual Nature of the Plant. Most of the early writers of continental 
Europe speak of Reboulia as monoecious, occasionally dioecious. On the 
British Isles, according to both Lett (23) and Cavers (5, 6, 7), it is usually 
dioecious, occasionally monoecious, in the latter case with the two kinds 
Figs. 23, 24. Transverse sections of male receptacles. Antheridia with mature 
sperms dotted, immature antheridia black. In figure 23, "x" indicates position of the 
youngest antheridia; female receptacle, with four archegonia, in the apical notch. Air 
chambers are shown anterior to the male receptacle. X 48. 
of receptacles at the apices of different branches, agreeing with the observa- 
tions of Leitgeb (21, 22). C. and R. Douin (10) claim Reboulia to be 
autoicous (monoecious), although it may appear dioecious by the abortion 
of either of the receptacles, but never paroicous. Howe (19) and Haupt 
(16) both find the American forms to be monoecious. The writer's obser- 
vations show that the thallus may be sterile, male, female, or bisexual, 
with both sex organs on different branches or on the same branch, and 
even in the same receptacle, a variable condition indicating plasticity in 
this feature. 
The Antheridium 
Origin. Haupt (16) says that "in all cases the antheridia develop 
strictly in acropetal succession from segments of the apical cell." The 
writer finds frequent exceptions to this rule. The first antheridia appear a 
few segments back of the apical cell and in the development of the receptacle 
are usually found near the median posterior margin (figs. 23, 24). An 
