1914] BURLINGAME—ARAUCARIA BRASILIENSIS 4907 
portion of the prothallus. In this way there is formed a sort of 
colony of free cells closely packed together but yet capable of easy 
separation. This condition gradually passes into the vacuolated 
condition of the inner part of the gametophyte, in which region 
walls are not formed for some time. In fact, it never becomes so 
solid as the outer parts. 
In about a month delicate walls have ac their appearance 
between the peripheral cells (figs. 31, 32), though no definite cells 
have yet been organized centrally (fig. 25). The exact method of 
wall-formation was not made out. The process is remarkably sug- 
gestive of the way in which walls are formed in cleavage furrows in 
certain lower plants. One such cell is formed for each nucleus. 
After the formation of these first walls, the succeeding ones in the 
outer part are laid down on cell plates formed on the spindles in the 
ordinary fashion. The outer cells are generally uninucleate, while 
the central cells, after they have become walled off, become multi- 
nucleate by the time the archegonia are mature. They also later 
contain considerable quantities of starch. 
In the further growth of the gametophyte, walls are formed on 
the spindles in the outer portion after each mitosis; in the central 
region wall-formation does not occur at this time. The transition 
from one region to the other is very gradual, and the walls thin out 
so gradually that it is almost or quite impossible to tell where there 
are actual walls. In fig. 31 are shown mitoses of both sorts. The 
one near the archegonium initial will have a wall formed on the 
spindle, while the one near the opposite border will not. Cell 
plates are formed in connection with the mitoses even before any 
walls are being formed on them (fig. 24). In the central region the 
nuclei are sometimes situated at the intersection of the larger 
strands and plates of cytoplasm and sometimes are suspended by 
much finer strands in the central region of the vacuolated spaces. 
Sooner or later these spaces, like the peripheral ones, form walls 
in the inclosing plates of cytoplasm and become cells. At the time 
of their inclosure by walls, they are commonly uninucleate. Later 
they frequently contain as many as 4-6 nuclei. Up to the time of 
the maturity of the archegonia the cytoplasm in all the cells of the 
gametophyte remains very scanty. 
