16 STRUCTURE AND LIFE-HISTORY OF HAY-SCENTED FERN. 



be but two layers of true cortex between endodermis and hypodermis . In 

 this case the outer layer has six large cells in a circle, and the inner layer 

 and hypodermis have twelve cells each. The sextant walls of the apex 

 thus persist, and may even at times be traced through the endodermis and 

 pericycle. Plainly this does not in any sense indicate a common origin of 

 endodermis and pericycle. 



In relation to the stem, the main root originates very near the apex, in that 

 layer of cells which will subsequently give rise to both endodermis and peri- 

 cycle (fig. 70). The rhizogenous cell is large and cubical. By three oblique 

 walls a tetrahedral initial is early cut out, and from this time onward it 

 behaves just as it would in a mature root. It has no fixed position in rela- 

 tion to the stem-initial. Beneath (centrad) the developing root-tissues a 

 great proliferation of stem-tissue takes place. The root is thus borne half- 

 way through the cortex, or farther, on a "pedicel" (figs. 59-61) while it 

 is of itself digesting away the outer cortex and forming a many-layered 

 cap. It finally emerges through a ragged opening in the cauline cortex 

 (fig. 102). 



During the elongation of the stem the vascular tissues connecting root 

 and stem are much deformed, with the following result: Tracing the 

 mature root inward, its stele passes obliquely half-way through the cortex 

 of the stem (fig. 102), then bends sharply backward, and fuses with the 

 stem stele. The cortex, endodermis, and pericycle of both organs are 

 smoothly continuous. But the root-xylem, after passing a little backward, 

 turns at an acute angle forward for a short distance. Some elements 

 become at once cauline, and run on forward. Others, by another sharp 

 bend, turn backward in joining the xylem of the stem. Rarely a tracheid 

 runs directly from the root into the stem without a double bend. Phloem 

 and conjunctive parenchyma follow parallel with the xylem. The depth 

 of these bends varies. In any case, those tracheids which are continuous 

 from root to stem must assume very peculiar shapes (figs. 58, 61, 62). 

 The bending occurs at an early stage of the development, before the cells 

 become lignified (fig. 61). When a root originates from a leaf-base it 

 passes out in a similar manner. A double bend occurs in the vascular 

 elements, but the folds are quite shallow. 



THE STEM. 



The rhizome is slender and cylindrical and more or less branched (fig. 

 3). A piece in my collection from Bucks County, Pennsylvania, grown in 

 loose loam, is 35 cm. long, with branches 15 cm. and 4 cm. long. Another 

 rhizome from Delaware County, Pennsylvania, is 8 cm. long to a fork; one 

 branch runs 23.5 cm. and forks into parts 4.5 cm. and 3 cm. long, respec- 

 tively; the other branch runs 19.5 cm. to a fork, with the parts 22 cm. and 

 13 cm. long. The diameter varies from 1.5 mm. to 4 mm., with a mean 

 of about 3 mm. When fresh the rhizomes are somewhat flexible, but the 



