1921] HAUPT—REBOULIA 67 
appear in the outer cell without a definite sequence, resulting in a 
filament of 4 cells (fig. 8). Vertical walls are then formed in two 
planes at right angles to each other, which usually are first developed 
in the basal tiers, or sometimes elsewhere (fig. 9). After the 
formation of the first vertical walls in the lower tiers, additional 
transverse divisions usually occur below, and as a consequence 
5 or 6 tiers of cells are formed (fig. 10). 
In Marchantia polymorpha Srras- 
BURGER (10) has reported that the 3 
transverse walls in the outer cell 
appear in centrifugal succession, al- 
though he shows no mitotic’ figures 
to prove this. Fig. 8 suggests that 
this may occur in Reboulia. STRAs- 
BURGER has also shown that the ver- 
tical walls appear in the 4-celled 
stage, but that no additional trans- 
verse walls are formed until the wall 
Fics. 6-8.—Fig. 6, series showing development of starch grains in plastids, 
1850; fig. 7, first division of outer segment of antheridial initial, <790; fig. 8, 
division of the lower segment of the outer cell, 790. 
and spermatogenous cells are differentiated. Marchantia therefore 
seems to be somewhat more advanced in this respect. DURAND 
(4), however, who also studied M. polymorpha, has found that 
additional transverse walls may follow the appearance of the 
vertical walls, but in no observed case did he find that they preceded 
the first vertical walls. 
Periclinal divisions next occur invariably in the 3 uppermost 
tiers of cells (figs. 11-13), separating the inner spermatogenous 
cells from the outer sterile wall cells. The cells in which no peri- 
clinal appears form the stalk. The further development of the 
