10 STRUCTURE AND LIFE-HISTORY OF HAY-SCENTED FERN. 
45°, as stated by Nageli and Leitgeb (1868, p. 76). The halves are next 
cut into quadrants by anticlinals at right angles to the first wall (figs. 11, 
12, 25). The succeeding walls in the quadrants are heterodromous and 
may be parallel to either of the preceding or be oblique (figs. 13, 25). 
No further regularity was found in the division of root-cap segments. 
The initial cell of the root is a triangular pyramid with its longest axis 
in the axis of the root (figs. 23, 27, 28). Lateral segments are cut off 
around the initial on one side after another in regular order. I noted ten 
roots (fig. 27) in which the succession of segments was counter-clockwise 
(proceeding from older to younger segments) and four in which it was 
clockwise, as one views the cell from its outer (capward) base. Each 
lateral segment divides first by a periclinal wall near its outer margin 
(figs. 14, 15, 23, 27-29). The next wall is a radial anticline which passes 
inward from near the middle of the first, and strikes one of the sides of 
the segment near its inner angle, dividing the inner cell into ‘‘sextants’’ 
(fig. 16, 11; segment 3 in figs. 27-29). Thus there is in each segment a 
larger (major) and a smaller (minor) sextant. In transverse section of 
the root we see the three major sextants meeting at the center of the sec- 
tion (figs. 29-33), with three alternating minor sextants which do not 
reach quite to the center. The ‘‘sextant wall’’ meets that side of the seg- 
ment which is adjacent to the next older segments, (kathodic wall) and is 
therefore katadromous. As all of the segments in any root are alike in 
this respect, the divisions are said to be homodromous. Soon after the 
sextant wall is formed in the inner part of the segment it is laid down 
also in the outer part (fig. 17; segment 4 in figs. 27-29). 
A second pericline is now laid down near the middle of each inner 
sextant cell (figs. 18, 23; segment 5 in figs. 27-30). As this wall forms 
the boundary between the plerome and outer tissues, it may be called the 
periplerome wall. Another periclinal laid down in the two outer sexants 
divides these into two layers, the definitive epidermis (piliferous layer) 
and hypodermis (fig. 19; segment 6 in figs. 27-31). Both of these tissues 
remain one-layered throughout. Subsequent divisions in them are all 
anticlinal, either radial or transverse (figs. 23; 27-33). Almost simul- 
taneously periclinal walls are formed on each side of the periplerome wall, 
near and parallel to it (figs. 14, 20, 21, walls v1 and vu; 23). In the 
majority of cases, however, the outer one seems to precede. The result- 
ing cells constitute the definitive endodermis and pericycle. The cells of 
the former are from the beginning flattened, of the latter nearly cubical 
(figs, 23, 31, 33). 
If we group the segments into cycles of three, beginning with the latest 
formed (¢f. figs. 27, 28), we find walls 1 and 1 (figs. 14-22) already in one 
or more of the youngest cycle. Walls 1, m1, and tv are found in the 
second cycle, and vi and vi in the second or third. In the second or 
