574 
MR. F. 0. BOWER ON THE COMPARATIVE MORPHOLOGY OF THE 
a two-sided apical cell, the segments from which divide so as to produce two longi¬ 
tudinal, marginal series ; these give rise at the apex of the phyllopodium to four pinnae, 
which appear in acropetal order, and themselves have marginal series of cells as in the 
Ferns. The development of the leaf of Pilularia not having been thoroughly inves¬ 
tigated, I have made a few observations upon it which show that it resembles that of 
Marsilia. 
Pilularia globulifera. 
The leaf of Pilularia has already been cited (p. 569) as an example of a simple phyllo¬ 
podium, without appendages of any sort. It has been pointed out by Al. Beaux * that 
it is connected with the Fern-type through Marsilia, in which the first formed leaves 
of the young seedling are without pinnae. 
In Pilularia, the conical, upturned apex of the horizontal axis bears members of 
three orders, which appear almost simultaneously in groups of three. They are, leaves 
which arise in two longitudinal rows on the dorsal t surface of the axis (Plate, 37, fig. 1, 
1-7); buds, or lateral axes, one of which arises below each of the leaves, that is nearer 
the ventral side of the axis, and in the same transverse plane (fig. 1 . b); and thirdly, 
roots formed endogenously, and similar in structure to those in Marsilia. One root 
is situated immediately below each bud (fig. 1, r). 
The leaf appears first as an outgrowth of a single cell of the axis ; in this cell 
divisions follow in regular succession cutting off two rows of segments from a two-sided, 
wedge-shaped, apical cell (figs. 2, 3). The position of the apical cell relatively to 
the axis appears, after the earliest stages, to be oblique, as seen in fig. 2. The 
further subdivision of the segments proceeds on the same plan as has been shown by 
Hanstein to obtain for Marsilia. The leaf assumes the circulate curvature at an 
early stage (fig. 1), and, as in other cases among the Filicineae, it is not coiled accurately 
in one plane. The activity of the apical cell is continued until the process of extension 
of the lower portion of the leaf, and the consequent unrolling of the young leaf begins. 
No clearly marked region of intercalary growth is to be found ; the process of extension 
is carried on uniformly throughout the tissues, beginning at the base and extending 
upwards. There is no continuation of the apical growth after the identity of the apical 
cell is lost, such as is found in the leaves of Ferns. Finally, the leaf develops from 
the first in a cylindrical form, and there is no prominent ridge to be found, nor any 
marginal series of cells similar to those in the Ferns and Marsilia. The cylindrical 
form is maintained to the extreme base. This leaf may thus be regarded as the 
simplest form of a phyllopodium, in which the mode of development is uniform from 
base to apex, and which bears no appendages. Though there is not any apparent 
* Neuere Unters. iiber d. Gatt. Marsilia u. Pilularia. 
t In speaking of horizontally growing axes, I use the term dorsal to signify the upper, and ventral the 
lower surfaces. In speaking of leaves, the term ventral is applied to the surface facing the axis, and 
dorsal to that which is turned away from the axis. This use of the terms is, however, obviously incon¬ 
sistent, though it is now generally adopted. 
