Mar., 1923] 
SHOWALTER — RICCARDIA PINGUIS 
159 
seen; sometimes, however, as many as eighteen are formed. The primary ventral cell, 
by a transverse division, produces a ventral canal cell and egg which are almost equal in size. 
The ventral canal cell disintegrates very soon after being formed, and 
its disintegration is followed by that of the neck-canal row. 
The most satisfactory account of archegonial development in any of the 
Jungermanniales (not including Sphaerocarpales) is that of Grim (1914) 
for Treubia insignis. Here the mother cell of the axial row divides, as in 
probably all the Hepaticae, into a central cell and a neck-canal mother cell. 
From the neck-canal mother cell there next arise successively four neck-canal cells. 
These undergo in the course of development a doubling to eight cells. These latter again 
divide so that we find in the fully grown archegonium sixteen neck-canal cells. During the 
formation of the eight neck-canal cells a division is likewise observed in the ventral tier of 
cells, that is, in the secondary central cell which has previously been changing slowly into 
a spherical form. This [division of the central cell] results in the formation of a smaller 
ventral canal cell and a considerably larger spherical egg. 
Of the Sphaerocarpales, Geothallus tuberosus has been studied by Camp¬ 
bell (1896), Sphaerocarpos texanus by Miss Rojas (1918), and 5 . Donnellii 
by Miss Hartman (1918). All three are of the Riccia type so far as concerns 
the development of the axial row. The mother cell of the axial row divides 
into a central cell and a neck-canal mother cell. The latter, by two suc¬ 
cessive divisions, forms four neck-canal cells, these divisions being followed 
by an unequal division of the central cell to form the egg and ventral canal 
cell (the consecutive order of divisions is not stated for Geothallus). 
The present state of our knowledge does not justify an extended gen¬ 
eralization on the development of the axial row in the liverworts. In all 
the Hepaticae described (not including the Anthocerotales, which differ 
only slightly), this row develops from a primary axial cell which divides 
first into a central cell and a neck-canal mother cell. The latter by succes¬ 
sive divisions gives rise to the neck-canal cells whose number is usually 
a power of two (occasional exceptions as to number in Riccardia, Pellia, 
Reboulia, and doubtless other forms). In the Jungermanniales studied 
the division of the central cell precedes the last division of the neck-canal 
cells (with possible exceptions in Pellia, according to Hutchinson, and in 
Pallavicinia, according to Haupt). In the Sphaerocarpales there are only 
two successive divisions of the neck-canal mother cell and its daughter 
cells, and these are completed before the division of the central cell. In the 
Marchantiales, the division of the central cell may be followed by one or 
more divisions in the neck-canal cells, as in Reboulia (Haupt, 1921), or it 
may occur after the last of these divisions, as in Riccia (Janczewski, Garber), 
or both conditions may be found in the same species, as in Marchantia 
(Durand). Which of these conditions is the more primitive, one can only 
conjecture. If we assume that the condition characteristic of the Junger¬ 
manniales is the more primitive, we might conclude that the last division 
of the neck-canal cells has been suppressed in the Sphaerocarpales and in 
