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 (cap ward) 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 vi and vii; 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 (,cf. figs. 27, 28), we find walls i and n (figs. 14-22) already in one 

 or more of the youngest cycle. Walls n, in, and iv are found in the 

 second cycle, and vi and vii in the second or third. In the second or 



