which, with a little care, may be seen the sections of two
fibro-vascular bundles. In the green zone are sometimes to be seen
colorless spots, sections of resin ducts, containing the resin so
characteristic of the tissues of the conifers.

[10] In most conifers the symmetrical form of the young tree is
maintained as long as the tree lives.

The general structure of the stem may be understood by making a series
of cross-sections through branches of different ages. In all, three
regions are distinguishable; viz., an outer region (bark or cortex)
(Fig. 76, _A_, _c_), composed in part of green cells, and, if the
section has been made with a sharp knife, showing a circle of little
openings, from each of which oozes a clear drop of resin. These are
large resin ducts (_r_). The centre is occupied by a soft white tissue
(pith), and the space between the pith and bark is filled by a mass of
woody tissue. Traversing the wood are numerous radiating lines, some
of which run from the bark to the pith, others only part way. These
are called the medullary rays. While in sections from branches of any
age these three regions are recognizable, their relative size varies
extremely. In a section of a twig of the present year the bark and
pith make up a considerable part of the section; but as older branches
are examined, we find a rapid increase in the quantity of wood, while
the thickness of the bark increases but slowly, and the pith scarcely
at all. In the wood, too, each year's growth is marked by a distinct
ring (_A_ i, ii). As the branches grow in diameter the outer bark
becomes split and irregular, and portions die, becoming brown and
hard.

The tree has a very perfect root system, but different from that of
any pteridophytes. The first root of the embryo persists as the main
or "tap" root of the full-grown tree, and from it branch off the
secondary roots, which in turn give rise to others.

The sporangia are borne on special scale-like leaves, and arranged
very much as in certain pteridophytes, notably the club mosses; but
instead of large and small spores being produced near together, the
two kinds are borne on special branches, or even on distinct trees
(_e.g._ red cedar). In the Scotch pine the microspores are ripe about
the end of May. The leaves bearing them are aggregated in small cones
("flowers"), crowded about the base of a growing shoot terminating the
branches (Fig. 77, _A_ [Male]). The individual leaves (sporophylls