2 STRUCTURE AND LIFE-HISTORY OF HAY-SCENTED FERN. 
the second by Van Teighem and Douliot in 1888. The latter authorities 
indicate that in some ferns (Péeris, Adiantum, Aneimia, etc.) the outer 
cell (figs. 14, 16, 17) may give rise to two or three layers of cortex in ad- 
dition to the epidermis (see table of cell-lineage in fern roots, p. 46). Such 
ferns are in the minority. The same writers state that in Agzisetum, 
Osmunda, and Todea the first periclinal wall is between the central cyl- 
inder and cortex, but that this is not the case in any other Pteridophytes 
which have a single initial in the root. 
I have found the account here given for Dennstedtia as to the origin of 
epidermis, hypodermis, cortex, and endodermis to apply equally to root-tips 
of Cibotium regale, Aspidium molle (fig. 48), Lygodium japonicum, Onoclea 
sensibilis (fig. 51), Ceratopteris thalictroides (fig. 50), and Aspidium mar- 
ginale (fig. 47). In Pteridium aquilinum and Didymochlena luniulata (fig. 
49) the epidermis and two layers of cortex are derived from the same part 
of the segment. 
Above the region of cell division in the root-tip there intervenes a brief 
region of elongation. Beyond this, viz, about 2.5 mm. from the apex, 
root-hairs appear. Each hair is 
: : T —Root-hairs. 
a cylindrical outgrowth from the Anke gone Gears 
lower (distal) end of an epidermal | yengtn. | diameter. Baas. 
cell. The cavities of cell and hair are 
continuous, and contain but one ie fi 
nucleus (fig. 252) lying variously 0.5+ 0.014 | Broken off. 
s 0.3+ 0.014 Do. 
in the wall-layer of protoplasm. ao o.o14 | Entire; immature? 
In functional hairs the nucleus is 
seen near the swollen apex. The 
walls of the hairs are thin, of a clear, brownish-yellow color, and are often 
molded around irregular particles of earth. Table 3 gives the exact 
dimensions. 
A transverse section of the region of functional root-hairs (figs. 34, 35, 
44) shows the epidermis, hypodermis, four or five (rarely three) layers of 
cortex and a well-defined endodermis. A single layer (rarely doubled in 
places) of pericycle surrounds the cylindrical, diarch bundle. Protoxylems 
abut directly upon the pericycle at diametrically opposite points, and 
between them lies a group of two to four (rarely five) large tracheids. 
Extending around within the pericycle from each side of each protoxylem 
is a row of three to seven sieve-tubes. Midway between the protoxylems 
and lying against the pericycle is the small-celled, dense protophloem. 
Between the phloem and xylem are cells of conjunctive parenchyma. 
The epidermis (piliferous layer of Van Tieghem, etc.) at the level we 
are speaking of is fully mature, and consists of cells four to six times as 
long as wide. In cross-section they are nearly isodiametric, of slightly 
variable depth and width, and bulging out a little on the outer side. The 
