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3 
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1898 ] THE LEAF AND SPOROCARP OF PILULARIA a 
intercellular spaces between the cells of the ground meristem 
and those of the hypodermis (a ¢, figs. 7-9) on the line of 
the median wall, of each section wall, and on the halving 
anticline of section I. The primary partition cells divide by 
periclines and thus increase in a radial direction as the leaf 
increases in diameter. At certain points the tips of these cells 
remain in contact with those of their fellows in adjoining sec- 
tions laterally (as at the median wall and halving anticline in 
fig. 8). When viewed in tangential section (fc, fig. 70) it is 
seen that each cell of the partition elongates tangentially and 
forms thus a protuberance at the upper end on one side and at 
the lower end of the cell on the other side. Then when the 
next transverse anticline is formed it is slightly oblique and 
forms two wedge-like cells, each with a protuberance on one end 
and none at the other (fig. zo). These cells soon elongate with 
the growth in length of the leaf, and cells are cut off from each 
which are not in contact with their fellows laterally (jg. If). 
Thus arise the longitudinal partitions which separate laterally 
the adjacent air canals. The protruding ends of the partition 
cells, which separate the divisions, at first short, of the same lon- 
gitudinal canal from each other, are finally cut off by oblique anti- 
clines (c p, fig 17) and form thus transverse partitions two cells 
broad from one longitudinal partition to the next. These cells 
do not divide further, as in Marsilia to form transverse parti- 
tions many cells in width, but elongate very greatly as the lon- 
gitudinal partitions separate by the growth in circumference of 
the leaf. The latter, however, are closer together at the point 
where joined by the transverse partitions, and thus each longitu- 
dinal partition, as seen in tangential section, has a zigzag course 
from the base to the apex of the leaf. Both kinds of partitions 
remain one cell in thickness throughout, and both are perfo- 
rated by pores, the “meats” of Meunier, which allow the free 
circulation of the enclosed air to all parts of the leaf. 
The stomata which are present on both the leaf and the 
sporocarp and the peculiar trichomes which cover all the younger 
parts (Mettenius ’46) have been carefully studied and figured 
