20 STRUCTURE AND LIFE-HISTORY OF HAY-SCENTED FERN. 
phloems present no differences. The inner pericycle is one to two, rarely 
three, cellsthick. Inner endodermis is like the outer in cross-sections, but 
seems to have longer cells (see table, p. 19). 
The layer of starchy medulla inside the vascular ring corresponds with 
that on the outside. In arhizome with six to eight layers outside, there are 
about seven inside. In another with three or four (mostly three) layers 
outside, there are two or three (mostly three) inside. But the inner cells 
are smaller than the outer (see table, p. 19). The inner sclerenchyma 
cells (sclerotic medulla) are longer and narrower than the outer, and have 
thicker and blacker walls (figs. 63, 64, 76, 77, 80). They form a core 
from twelve to twenty-two cells in diameter. 
The above type of stem is called by Gwynne-Vaughan (1901) a solenostele 
(adj. solenostelic) and by Jeffrey (1897) an amphiphloic siphonostele. The 
description may serve as a definition of these terms. 
At the node (figs. 3, 4, 66) the cylindrical leaf-base springs from the 
slightly larger stem at a right or acute angle, usually without altering the 
size or shape of the stem. Occasionally the stem is slightly enlarged 
below the node, and rarely there is a slightly prominent ridge between leaf 
and stem, as at a fork. 
The leaf-trace or vascular bundle of the leaf (petiolar meristele) leaves 
the stem as a trough-like band (horseshoe-shaped in transverse section) 
which is of the same thickness as the wall of the vascular tube of the stem 
(fig. 82). The concavity of the trough faces obliquely upward and forward 
in most leaves. But where the leaf-insertion is ventral (figs. 83-87) or 
lateral the trace faces directly upward. When the insertion is dorsal the 
trace faces directly forward. At the place where the leaf-trace leaves the 
tubular vascular system of the stem a distinct leaf-gap occurs (fig. 82). 
This is a narrow slit in the stem bundle, through which the medullary and 
cortical tissues become continuous. The gaps differ in shape and in their 
exact relation to the leaf-trace. One gap is 11 mm. long and 1.2 mm. 
wide, with acute ends, and with the leaf-trace attached near the middle of 
the ventral side. Anotheris 14mm. by 1 mm. A third is 1.8 mm. by 
0.3 mm., rounded at both ends, with the leaf-trace occupying nearly all of 
one side. The average size (of ten) is 5.45 mm. long and 0.53 mm. wide. 
Usually the anterior end is rounded and the posterior end tapering and 
acute, with the leaf-trace attached along one side, at or near the anterior 
end. Such a gap is figured by Gwynne-Vaughan (1903, plate 33, fig. 1). 
When the leaf-insertion is dorsal the trace arises symmetrically from the 
rounded posterior end of the gap. Lateral leaf-traces differ scarcely at all 
in their origin from the usual dorso-lateral type. Ventral leaves, spring- 
ing from a fork, are symmetrically attached to each arm of the stem (figs. 
83-87). The trace lies like a trough with its concavity upward. Approach- 
ing such a nodal fork along the main stem, the stele first becomes wide 
and flat. Thena slit is found on the upper side, and as the branches 
