Overwinteringterminal bud of sugar maple x8. A nearby lateral branch bud is alsovisible. Terminal bud scales are easily seen. These scales fall off asthe stem elongates leaving behind a set of terminal bud scale scars.
Terminalbud scale scars on sugar maple x15. A set of scars such as thesecompletely surround the stem, unlike leaf scars. They are found alongthe stem where one growth year ends and the next begins. The mostrecent year's growth shown here is to the right.
Lenticelson the surface of a twig x15. These allow gas exchange through thewater and gas proof cork layer that covers small twigs.
Leafscar x10. The "smiley face" is a curved row of vein scars where theveins once entered the leaf through the abscission zone. A dormantlateral branch bud is immediately above the leaf scar on the left sideof the photograph.
Helianthusyoung stem xs x40. A typical dicot stem with a ring of vascularbundles. Everything you see here is primary tissue because the vascularcambium has not yet become active.
Lilliumstem xs x40. A typical monocot stem with scattered vascularbundles.
Zeamays stem xs x40. Another typical monocot stem with scatteredvascular bundles.
Cornvascular bundles scattered within the parenchyma ground tissue ofthe stem x100. The phloem of each bundle is toward the top in thisphotograph. The two large cells within each bundle are vessels. Thewhite area in the bottom center of each bundle is a large intercellularspace that functions as a vessel. This tube-shaped intercellular spacewas formed during the bundle's growth when some cells of the bundlecontinued to elongate while some nearby xylem cells could not elongatebecause they had become lignified. The result was a tearing apart ofthe lignified cells.
Asingle Helianthus vascular bundle from a ring of vascularbundles in a dicot stem x100. Note collenchyma cells near the outsideof the stem and parenchyma cells near the center. The vascular bundleshows from the outside in fibers, primary phloem, vascular cambium, andprimary xylem. The large red staining cells within the xylem are vesselelements. The vascular cambium of this bundle is just starting tobecome active and has produced a few radially alligned rows of cells.Eventually the primary xylem and phloem of this bundle will be pushedapart by the production of secondary xylem and phloem by the vascularcambium.
YoungColeus stem xs x40. Some parenchyma cells betweenvascular bundles have become meristematic linking the vascular cambiumof the large vascular bundle (arrow) with adjacent smaller vascularbundles. The result is a complete ring of radially alligned cellscircling the stem and separating the pith from the cortex. Theseradially alligned cells will become secondary xylem and phloem.
Alog split radially (radial section) illustrating heartwood,sapwood, pith, and a lateral branch buried in the secondary xylem ofthe log.
Pawpawstem xs x100 with a growth ring. The large cells are vessels. Thesmall diameter cells are mainly fibers. In which direction is theoutside of the stem, to the right or to the left?
Monocotstem xs with secondary vascular bundles x40. This is a palm-likeplant (Beaucarnia) in the family Agavaceae. The entire (butmainly the outer) cortex remains meristematic and produces secondaryvascular bundles, resulting in an increase in stem diameter. Inmonocots, there is no single vascular cambium, like that found invirtually all other plant groups with secondary growth.
Pinusone year old stem xs x100. You can see secondary xylem, vascularcambium, secondary phloem, cortex, and a cork cambium. The cellsimmediately outside the cork cambium have been cut off from water andare dead, appearing here to be clear with no cytoplasm. There are tworesin ducts, each surrounded by small secretory cells, within thecortex.
Pinuswood xs x100. A growth ring and resin duct are visible in thiscross section. Most of the cells are tracheids. In which direction isthe outside of the stem, towards the top or bottom of the illustration?
Pinuswood ts x100. Short rays one cell in width are seen in thistangential section.
Corklayers xs x40 on the outer surface of an oak (Quercus)stem. Several cork cambia are visible. The upper part of theillustration shows the outer secondary phloem where new cork cambia andcork layers will soon form.
Tylosesin an oak vessel rs x100. A large vessel filled with tyloses(plugs) in the heartwood of an oak tree. A smaller functioning (notyloses) vessel composed of several vessel elements is on the left.
Oakwood ts x100. A very tall wide ray and numerous small rays arevisible in tangential section. The blue cells are all fibers.
Oakvascular cambium xs x400. The blue cells are secondary xylem andthe larger white cells are secondary phloem. The vascular cambiumextends from right to left within the small rectangular cells. Notethat rays extend from xylem through the cambium and into the phloem.
Oakxylem and phloem xs x40. A lower magnification view of the previousillustration. The solid blue area of cells are fibers and vessels ofthe secondary xylem. Immediately outside of the blue staining xylem isthe vascular cambium. The secondary phloem has blue staining fiberswithin it. Note that the older (outer) secondary phloem is becomingcrushed. Only the most recently formed phloem near the vascular cambiumactually functions as phloem.
Tiliayoung stem xs x100. From the bottom to the top, you can seeepidermis (sloughing off), cork, cortex, fibers that used to be on theouter part of a vascular bundle, primary phloem, secondary phloem withrows of fibers, vascular cambium, and secondary xylem. The old vascularbundles are still partially separated in the area of the phloem by pithrays made of parenchyma cells.
Tiliacork cambia and phloem xs x100. The wedge shaped structures areprimary and secondary phloem. Secondary xylem is just visible at thetop of the photograph. At least two and probably several more corkcambia can be seen at successively deeper layers within the phloem.
Tiliawood xs x400. A ray runs vertically and a growth ring can be seenhorizontally. In which direction is the outside of the stem, toward thetop or bottom of the photograph? The large cells are vessels. Smalldiameter cells are mostly small vessels, fibers, and wood parenchyma.
Tiliawood tangential section x40. Two very tall rays each 2 cells wideare visible on the right and left sides of the photograph. The othercells are vessels, thin walled fibers, and wood parenchyma (smallrectangular vertically aligned cells).