Mar., 1923] 
SHOWALTER — RICCARDIA PINGUIS 
157 
The cells of the axial row show an alveolar cytoplasmic structure, the 
alveoli becoming larger as the cells grow older. My preparations in general 
do not show the plastids clearly, and only rarely can these structures be seen 
distinctly in any of the cells of the axial row. They are, however, visible 
in some preparations, both in the cells of the axial row and in fairly young 
embryos. A few nearly mature eggs show bodies which are probably 
plastids, and if, as Miss Clapp reports, starch grains are present in the 
mature egg, there seems little reason to doubt that plastids are present in the 
egg and zygote throughout their history. 
Occasionally, instead of three penultimate cells (central cell and two 
neck-canal cells) in the axial row at the stage shown in figure 24, Plate 
XVII, as described above, four are formed. All of these four divide in 
acropetal succession as do the three of the more frequent type, and this 
division results in the formation of an egg, a ventral canal cell and six neck- 
canal cells (figs. 34-37, PL XVIII). (See also Clapp, 1912, and Florin, 1918.) 
In the two archegonia represented in figures 36 and 37, there is no indication 
of a cell division following the last nuclear division in the neck-canal cells, 
but the egg and ventral canal cell have evidently begun to disintegrate and 
these cases cannot be regarded as normal. Axial rows of four penultimate 
cells are not sufficiently frequent to justify an unqualified statement as to 
the manner of the formation of the fourth penultimate cell, but the evidence 
available seems to indicate that the uppermost cell of the three-celled 
axial row grows and divides before, or at about the same time that, the 
central cell divides into the egg and ventral canal cell (figs. 34, 35). Another 
variation of similar type but of inverse order is represented by a single case 
(fig. 32) in which the usual first division of the neck-canal mother cell was 
omitted, thus giving rise to only two penultimate cells, one of which has 
divided to form a typical egg and ventral canal cell and the other is in prep¬ 
aration for division to form a neck-canal row of only two cells. 
The exact sequence of divisions in the development of the axial row has 
not been followed in a large number of the Hepaticae, but certain incom¬ 
plete accounts seem to indicate that in some of the other Anacrogynae that 
development is similar to this in Riccardia. Janczewski (1872) described 
the central cell of Pellia epiphylla as remaining undivided while its sister 
divides to form eight (rarely nine) neck-canal cells. The central cell then 
divides to form the egg and ventral canal cell, this division being followed 
by a doubling of the number of cells in the neck and in the neck-canal row, 
making sixteen (occasionally eighteen) of the latter. He does not say 
whether the division of the central cell is equal or unequal, nor does he explain 
the manner of the doubling of the number of cells in the neck-canal row. If, 
as seems probable, this doubling is brought about by a division of each of 
the eight (or nine) cells, the egg and ventral canal cell, as in Riccardia, are 
the oldest of the ultimate cells of the canal row. Hutchinson (1915) reports 
that the maximum number of neck-canal cells he could find in Pellia epiphylla 
