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bud of sugar maple x8. A nearby lateral branch
bud is also visible. Terminal bud scales are easily seen.
These scales fall off as the stem elongates leaving
behind a set of terminal bud scale scars.
Terminal bud scale scars
on sugar maple x15. A set of scars such as these
completely surround the stem, unlike leaf scars. They are
found along the stem where one growth year ends and the
next begins. The most recent year's growth shown here is
to the right.
the surface of a twig x15. These allow gas exchange
through the water and gas proof cork layer that covers
x10. The "smiley face" is a curved row of vein
scars where the veins once entered the leaf through the
abscission zone. A dormant lateral branch bud is
immediately above the leaf scar on the left side of the
apical meristem x40 showing lots of leaf
apical meristem x40. Note the immature
vascular bundles in the stem extending as veins into
apical meristem close up x100. Note the leaf
primordia. Also note the two lateral branch bud meristems
immediately above the large leaves.
young stem xs x40. A typical dicot stem with a
ring of vascular bundles. Everything you see here is
primary tissue because the vascular cambium has not yet
stem xs x40. A typical monocot stem with
scattered vascular bundles.
Zea mays stem
xs x40. Another typical monocot stem with
scattered vascular bundles.
Corn vascular bundles
scattered within the parenchyma ground tissue of the stem
x100. The phloem of each bundle is toward the top in this
photograph. The two large cells within each bundle are
vessels. The white area in the bottom center of each
bundle is a large intercellular space that functions as a
vessel. This tube-shaped intercellular space was formed
during the bundle's growth when some cells of the bundle
continued to elongate while some nearby xylem cells could
not elongate because they had become lignified. The
result was a tearing apart of the lignified cells.
A single Helianthus
vascular bundle from a ring of vascular
bundles in a dicot stem x100. Note collenchyma cells near
the outside of the stem and parenchyma cells near the
center. The vascular bundle shows from the outside in
fibers, primary phloem, vascular cambium, and primary
xylem. The large red staining cells within the xylem are
vessel elements. The vascular cambium of this bundle is
just starting to become active and has produced a few
radially alligned rows of cells. Eventually the primary
xylem and phloem of this bundle will be pushed apart by
the production of secondary xylem and phloem by the
stem xs x40. Some parenchyma cells between
vascular bundles have become meristematic linking the
vascular cambium of the large vascular bundle (arrow)
with adjacent smaller vascular bundles. The result is a
complete ring of radially alligned cells circling the
stem and separating the pith from the cortex. These
radially alligned cells will become secondary xylem and
illustrating cross section (xs), radial section (rs), and
tangential section (ts) cuts.
A log split radially
(radial section) illustrating heartwood, sapwood, pith,
and a lateral branch buried in the secondary xylem of the
Pawpaw stem xs
x100 with a growth ring. The large cells are vessels. The
small diameter cells are mainly fibers. In which
direction is the outside of the stem, to the right or to
Monocot stem xs with
secondary vascular bundles x40. This is a palm-like plant
(Beaucarnia) in the family Agavaceae. The entire (but
mainly the outer) cortex remains meristematic and
produces secondary vascular bundles, resulting in an
increase in stem diameter. In Monocots there is no single
vascular cambium like that found in virtually all other
plant groups with secondary growth.
Monocot secondary vascular
bundles x100. These Beaucarnia
secondary vascular bundles have a small patch of phloem
in the center that is completely surrounded by xylem.
year old stem xs x100. You can see secondary
xylem, vascular cambium, secondary phloem, cortex, and a
cork cambium. The cells immediately outside the cork
cambium have been cut off from water and are dead,
appearing here to be clear with no cytoplasm. There are
two resin ducts, each surrounded by small secretory
cells, within the cortex.
xs x100. A growth ring and resin duct are
visible in this cross section. Most of the cells are
tracheids. In which direction is the outside of the stem,
towards the top or bottom of the illustration?
ts x100. Short rays one cell in width are seen
in this tangential section.
Cork layers xs
x40 on the outer surface of an oak (Quercus)
stem. Several cork cambia are visible. The upper part of
the illustration shows the outer secondary phloem where
new cork cambia and cork layers will soon form.
Tyloses in an oak vessel
rs x100. A large vessel filled with tyloses
(plugs) in the heartwood of an oak tree. A smaller
functioning (no tyloses) vessel composed of several
vessel elements is on the left.
Oak vascular cambium and
phloem rs x400. The vascular cambuium is
within the narrow white cells center-right. Phloem with
blue staining sieve areas is center-left.
Oak wood ts
x100. A very tall wide ray and numerous small rays are
visible in tangential section. The blue cells are all
Oak vascular cambium xs
x400. The blue cells are secondary xylem and the larger
white cells are secondary phloem. The vascular cambium
extends from right to left within the small rectangular
cells. Note that rays extend from xylem through the
cambium and into the phloem.
Oak xylem and phloem xs
x40. A lower magnification view of the previous
illustration. The solid blue area of cells are fibers and
vessels of the secondary xylem. Immediately outside of
the blue staining xylem is the vascular cambium. The
secondary phloem has blue staining fibers within it. Note
that the older (outer) secondary phloem is becoming
crushed. Only the most recently formed phloem near the
vascular cambium actually functions as phloem.
young stem xs x100. From the bottom to the top
you can see epidermis (sloughing off), cork, cortex,
fibers that used to be on the outer part of a vascular
bundle, primary phloem, secondary phloem with rows of
fibers, vascular cambium, and secondary xylem. The old
vascular bundles are still partially separated in the
area of the phloem by pith rays made of parenchyma cells.
cambia and phloem xs x100. The wedge shaped
structures are primary and secondary phloem. Secondary
xylem is just visible at the top of the photograph. At
least two and probably several more cork cambia can be
seen at successively deeper layers within the phloem.
xs x400. A ray runs vertically and a growth
ring can be seen horizontally. In which direction is the
outside of the stem, toward the top or bottom of the
photograph? The large cells are vessels. Small diameter
cells are mostly small vessels, fibers, and wood
tangential section x40. Two very tall rays
each 2 cells wide are visible on the right and left sides
of the photograph. The other cells are vessels, thin
walled fibers, and wood parenchyma (small rectangular
vertically aligned cells).
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