SPOROPHYTE. 11 



third cycle of segments longitudinal radial anticlines are also formed in 

 the outer members of the segment, dividing the sextants into halves (figs. 

 21, 22, viu). As yet each segment consists of but one layer of cells. 

 Transverse anticlines occurring throughout the segment in the third or 

 fourth cycle make it two-layered (fig. 23). A second series of divisions 

 in the same plane cuts the outer tissues (epidermis, hypodermis, cortex) 

 into four vertical layers. These cleavages occur first in the epidermis, 

 but their order of sequence is rapid and apparently varied. The pericycle 

 is late in becoming divided; and the endodermis of a certain pair of oppo- 

 site sextants lacks the radial division for a long time, as will be described 

 in speaking of the origin of lateral rootlets. 



The large cell remaining between the endodermis and hypodermis (figs. 

 14, 20, 21, 23) gives rise to all of the cortex. After its transverse anti- 

 clinal division it rapidly undergoes one to three periclinal and as many 

 radial divisions. The periclinals probably take place in centrifugal order. 

 The result is a cortex of two to four concentric layers, each with 14 to 24 

 cells. The last divisions are complete in the fourth, or at least the fifth 

 cycle of segments {cf. figs. 28-33). 



The triangular cells lying within the pericycle (fig. 21) divide either 

 by a periclinal wall into two parts or by two tangential walls into three 

 parts (figs. 22, 29-31). The tips of the three major sextants and of one 

 minor (occasionally two) become tracheids of the metaxylem. The cells 

 between the tracheids and the pericycle of this minor and of the major 

 opposite to it become protoxylem cells (figs. 14, 22, 29-33); the inter- 

 mediate parts of the other two majors, and all within the pericycle in the 

 two remaining minors (with the exception noted above) go to form phloem 

 (figs. 14, 22, 29-33). 



As the elements elongate, the transverse limits of the segments are 

 soon obliterated (fig. 23). Four or at most five cycles only can be recog- 

 nized. The sextants, however, may often be distinguished until quite a 

 late period (fig. 33). 



The above-described order of the early divisions of the segment (walls 

 i to vn, figs. 14-22) is easily followed in its main outlines in good serial 

 sections of any leptosporangiate fern root. But English and German 

 text-books* still adhere unanimously to the statement of Nageli and 

 Leitgeb that the first division in the segment is the sextant wall, fol- 

 lowed by that which separates periblem and plerome. The first error was 

 corrected by Lachmann (1885; 18S7',Jide Van Tieghem and Douliot), and 



*Nageli and Leitgeb, 1865, 1868; Pteris Campbell, 1895, p. 328-329, fig. i65A ; 1905 



hastata, plate 14, fig. 7. p. 333. 



Sachs, 1875, pp. 124-125, fig. io2A. Strasburger, 1897, pp. 31 1-313, figs. 139, 140. 



De Bary, 1884, pp. 18-19, ^g 8 - 7 A i 8A - Sadebeck, 1898, p. 61, fig. 4iA. 



Goebel, 1887, pp. 214-215, fig. 162. Strasburger, Noll, etc., 1898, pp. 150-151, 

 Bower, 1889. fig. 165. 



Vines, 1894, pp. 149-150, figs. 114, 115- Haberlandt, 1904, p. 74, fig. 14. 



