Leaf and Sporocarp in Marsilia qnadrifolia , L. 121 
according to Hofmeister (’62) and Klein (’84), the position of 
the two-sided apical cell is transverse to the stem. 
This apical cell of the leaf in Marsilia continues its growth 
and activity, cutting off segments alternately toward the right 
and left of the young leaf, which has its ventral . side facing 
toward the stem-apex. When about fifteen or sixteen pairs 
of segments have been formed, the activity of the apical cell 
is ended, probably by a periclinal wall like that seen by 
Sadebeck (’73), Kny (’75), and Bower (’84) in other Lepto- 
sporangiates, and that to be described later in the sporocarp 
of Marsilia. The great regularity of the segments of the 
leaf in Marsilia , as well as the fact that certain of the cells 
remain of the full length of the segment (Fig. 3), make it 
possible to determine quite definitely the number of segments 
formed (Fig. 2). The only doubt is in regard to the first 
segments, some of which fuse with the tissue of the stem, 
and it is thus not certain that the segment numbered 1 in 
Fig. 2 is not really the second one. The young leaf is about 
1 mm. long and -15 mm. in diameter at the base when the 
activity of the apical cell ceases, and is a slightly tapering 
conical organ curved upward (Fig. 2) and ventrally over the 
stem-apex. It is almost exactly circular in cross-section 
until the formation of the pinnae begins, and is not at all 
spatulate as described by Hanstein (’65) in M. Drummondii , 
and by Campbell (’96). 
The segments of the apical cell of the leaf, or ‘ primary 
marginal cells ’ of Hanstein (’65) and Sadebeck (’74), are 
nearly semicircular blocks with the upper and lower surfaces 
slightly concave toward the apex (Figs. 4-6). The first 
division-wall appearing in these segments is a longitudinal 
and radial anticline (/, Fig. 6), cutting off about one-third 
of the segment toward the dorsal side to form what we may 
call a section , and leaving on the ventral side a secondary 
marginal cell. Wall I is apparently the ‘ tangential wall ’ of 
Sadebeck (’74), and section I is the ‘ Schichtzelle * of Hanstein 
(’65), but this terminology does not seem appropriate when 
the real position of this and later section-walls is taken into 
K 2 
