1918] HAUPT—PALLAVICINIA 527 
the forward portion is slightly arrested, resulting in greater protec- 
tion from behind. It seems a perfectly logical step from the 
antheridial condition in Pallavicinia to that of one of the simpler 
acrogynous Jungermanniales, such as Porella, in which case the 
coverings are longer and more leaflike in appearance. 
Further growth of the antheridium corresponds to that of the 
other anacrogynous Jungermanniales. During the 2 or 3 mitoses 
preceding the formation of the sperm mother cells, the cell walls of 
the spermatogenous mass gradually disappear and abundant muci- 
lage surrounds the dividing protoplasts. Walls around the sperm 
mother cells were evident, but it could not be determined whether 
they had been laid down by the mother cell protoplasts, or rep- 
resented the remaining cellulose which had not become mucilage. 
* The sperm mother cells produce two sperms, each with little cyto- 
plasm, and separated by a very thin wall. The nuclei were so small 
that it was not possible to study the details of spermatogenesis. 
The development is probably the same as that of Pallavicinia Zol- 
lengeri, described by CAMPBELL and WILLIAMs (1). 
ARCHEGONIA 
The earliest stages in the development of the archegonial group 
were not present in the material studied. A group of initials seems 
to arise a short distance back of the apical cell, directly above the 
midrib on the dorsal side of the thallus. This group presently 
becomes surrounded by an annular upgrowth of the thallus, which 
becomes the involucre. The apical cell is not checked by the 
development of the archegonia, but continues the growth of the 
thallus, so that often 2 or 3 groups may be produced along the mid- 
rib, separated by sterile areas. The archegonial group continues 
to produce archegonia up to the time of fertilization, many young 
sex organs frequently being found with mature ones. Two-celled 
mucilage hairs are abundantly produced. Twenty to 30 arche- 
gonia usually occur in a group. 
The archegonium, like the antheridium, arises as a papillate 
projection from one of the cells inclosed by the involucre. A trans- 
verse wall cuts off a basal cell, which remains within the thallus, 
and an outer cell, which is freely exposed (fig. 10). The latter 
