a section is shown in Figure 82, _I_.

The body of the leaf is made up of chlorophyll-bearing cells of
irregular shape and with large air spaces between (_H_, _m_). The
veins traversing this tissue are fibro-vascular bundles of a type
structure similar to that of the stem, which will be described
presently.

The stem is made up principally of large cells with thin walls,
which in cross-section show numerous small, triangular,
intercellular spaces (_i_) at the angles. These cells contain,
usually, more or less starch. The fibro-vascular bundles (_C_) are
nearly triangular in section, and resemble considerably those of the
field horse-tail, but they are not penetrated by the air channel,
found in the latter. The xylem, as in the pine, is toward the
outside of the stem, but the boundary between xylem and phloem is
not well defined, there being no cambium present. In the xylem are a
number of vessels (_C_, _tr._) at once distinguishable from the
other cells by their definite form, firm walls, and empty cavity.
The vessels in longitudinal sections show spiral and ringed
thickenings. The rest of the xylem cells, as well as those of the
phloem, are not noticeably different from the cells of the ground
tissue, except for their much smaller size, and absence of
intercellular spaces.

The structure of the leaves of the perigone is much like that of the
green leaves, but the tissues are somewhat reduced. The epidermis of
the outer side of the sepals has breathing pores, but these are
absent from their inner surface, and from both sides of the petals.
The walls of the epidermal cells of the petals are peculiarly
thickened by apparent infoldings of the wall (_B_), and these cells,
as well as those below them, contain small, yellow bodies
(chromoplasts) to which the bright color of the flower is due. The
red specks on the base of the perigone leaves, as well as the red
color of the back of the sepals, the stalk, and leaves are due to a
purplish red cell sap filling the cells at these points.

The filaments or stalks of the stamens are made up of very delicate
colorless cells, and the centre is traversed by a single
fibro-vascular bundle, which is continued up through the centre of
the anther. To study the latter, thin cross-sections should be made
and mounted in water. Each of the four sporangia, or pollen sacs, is
surrounded on the outside by a wall, co