Stems

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  • Overwintering terminal 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.
  • Lenticels on the surface of a twig x15. These allow gas exchange through the water and gas proof cork layer that covers small twigs.
  • Leaf scar 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 photograph.
  • Elodea apical meristem x40 showing lots of leaf primordia.
  • Coleus apical meristem x40. Note the immature vascular bundles in the stem extending as veins into leaves.
  • Coleus apical meristem close up x100. Note the leaf primordia. Also note the two lateral branch bud meristems immediately above the large leaves.
  • Helianthus 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 become active.
  • Lillium 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 vascular cambium.
  • Young Coleus 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 phloem.
  • Wood block 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 log.
  • 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 the left?
  • 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.
  • Pinus one 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.
  • Pinus wood 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?
  • Pinus wood 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 fibers.
  • 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.
  • Tilia 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.
  • Tilia cork 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.
  • Tilia wood 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 parenchyma.
  • Tilia 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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