Anatomy of stem: secondary structure Introduction to Botany. Lecture 7 Alexey Shipunov Minot State University September 10th, 2010 Shipunov BIOL 154.7
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Anatomy of stem: secondary structure
Introduction to Botany. Lecture 7
Alexey Shipunov
Minot State University
September 10th, 2010
Shipunov BIOL 154.7
Anatomy of stem: secondary structure
More about plant classification
Mosses (Bryophyta)Ferns and allies (Pteridophyta)Seed plants (Spermatophyta)
Conifers (Pinopsida)Other classes of seed plantsAngiosperms (Magnoliopsida)
Monocots (Liliidae)Other subclasses of angiosperms (“dicots”)
Shipunov BIOL 154.7
Anatomy of stem: secondary structure
Outline
1 Anatomy of stem: secondary structureAnatomy of mature stemStructure of wood
Shipunov BIOL 154.7
Anatomy of stem: secondary structureAnatomy of mature stemStructure of wood
Vascular cambium
In many plants, residuals of procambium transform intofascicular cambiumParenchyma cells between vascular bundles produceinter-fascicular cambium
Shipunov BIOL 154.7
Anatomy of stem: secondary structureAnatomy of mature stemStructure of wood
Vascular bundle
Shipunov BIOL 154.7
Anatomy of stem: secondary structureAnatomy of mature stemStructure of wood
Vascular cylinder
Shipunov BIOL 154.7
Anatomy of stem: secondary structureAnatomy of mature stemStructure of wood
Gene alternates cylinder and bundles
The COV mutant of Arabidopsis (after Parker et al., 2003)
Shipunov BIOL 154.7
Anatomy of stem: secondary structureAnatomy of mature stemStructure of wood
Cork cambium and origin of bark
Bark is everything outside vascular cambium, therefore,bark = secondary phloem + peridermEach year new layer of cork cambium appear fromparenchyma cells of secondary phloemConsequently, bark consists of multiple and mostly unevenlayers
Shipunov BIOL 154.7
Anatomy of stem: secondary structureAnatomy of mature stemStructure of wood
Renewal of bark in sea buckthorn (Hippophaërhamnoides)
Shipunov BIOL 154.7
Anatomy of stem: secondary structureAnatomy of mature stemStructure of wood
Secondary phloem
Forms outside vascular cambiumRich of fibersDoes not form annual ringsHas rays of parenchyma cells, sometimes wedge-shaped(dilated)
Shipunov BIOL 154.7
Anatomy of stem: secondary structureAnatomy of mature stemStructure of wood
Dilated rays of beech (Fagus sp.)
Shipunov BIOL 154.7
Anatomy of stem: secondary structureAnatomy of mature stemStructure of wood
Periderm
Periderm is the product of cork cambium99% of periderm is a phellem (cork cells), thick outsidelayerPhelloderm is a tiny layer of living cells inside of corkcambium
Shipunov BIOL 154.7
Anatomy of stem: secondary structureAnatomy of mature stemStructure of wood
Formation of bark zone in medlar (Mespilusgermanica)
Shipunov BIOL 154.7
Anatomy of stem: secondary structureAnatomy of mature stemStructure of wood
Lenticels
Lenticels are specialized regions of periderm; they supplystem cells with oxygenIn order to produce lenticel, some cells of cork cambiumdivide and grow much faster than others
Shipunov BIOL 154.7
Anatomy of stem: secondary structureAnatomy of mature stemStructure of wood
Lenticel of elderberry (Sambucus sp.)
Shipunov BIOL 154.7
Anatomy of stem: secondary structureAnatomy of mature stemStructure of wood
Secondary structure
Shipunov BIOL 154.7
Anatomy of stem: secondary structureAnatomy of mature stemStructure of wood
Primary structure (from previous lecture)
Shipunov BIOL 154.7
Anatomy of stem: secondary structureAnatomy of mature stemStructure of wood
Hyperstele
Mature stem with secondary structure often called “hyperstele”(Cronk, 2009)Shipunov BIOL 154.7
Anatomy of stem: secondary structureAnatomy of mature stemStructure of wood
Bark and wood
Shipunov BIOL 154.7
Anatomy of stem: secondary structureAnatomy of mature stemStructure of wood
Secondary xylem and rays
Secondary xylem, or wood, is the product of vascularcambiumSome cambium cells are fusiform initials; they form axialvessel elementsOther cambium cells are ray initials; they form rays(parenchyma + tracheids)Rays provide horizontal transport of water; axial systemprovide vertical transport
Shipunov BIOL 154.7
Anatomy of stem: secondary structureAnatomy of mature stemStructure of wood
Fusiform and ray initials
Shipunov BIOL 154.7
Anatomy of stem: secondary structureAnatomy of mature stemStructure of wood
Three planes of view
Transverse* (cross-section)Radial (longitudinal section from center to periphery andperpendicular to stem surface)Tangential (longitudinal section parallel to stem surface)
Shipunov BIOL 154.7
Anatomy of stem: secondary structureAnatomy of mature stemStructure of wood
Three plains of maple (Acer sp.) stem
Shipunov BIOL 154.7
Anatomy of stem: secondary structureAnatomy of mature stemStructure of wood
Earlywood and latewood
Earlywood (springwood) contains more parenchyma andoften have larger vessel elementsLatewood (summerwood) often have small vesselelements and looks darker
Shipunov BIOL 154.7
Anatomy of stem: secondary structureAnatomy of mature stemStructure of wood
Diffuse and ring porous wood
In ring porous wood (like in red oak) bigger vesselelements concentrate in earlywoodIn diffuse porous wood larger vessel elements spreadacross early- and latewood (American elm)
Shipunov BIOL 154.7
Anatomy of stem: secondary structureAnatomy of mature stemStructure of wood
Diffuse and ring porous wood in two species ofcinquefoil (Potentilla spp.)
Shipunov BIOL 154.7
Anatomy of stem: secondary structureAnatomy of mature stemStructure of wood
Annual rings
Interleaving early- and latewood from to sequential yearsform an impression of annual ring“Ring” is just a layer of darker (i.e., smaller) cellsTropical trees do not form annual rings
Shipunov BIOL 154.7
Anatomy of stem: secondary structureAnatomy of mature stemStructure of wood
Annual rings in juniper (Juniperus sp.)
Shipunov BIOL 154.7
Anatomy of stem: secondary structureAnatomy of mature stemStructure of wood
Sapwood and heartwood
Sapwood is a peripheral layer of working xylem, it usuallyhas relatively light colorHeartwood is a central, non-functional, old, dark-coloredxylem
Shipunov BIOL 154.7
Anatomy of stem: secondary structureAnatomy of mature stemStructure of wood
Sapwood and heartwood of European pine (Pinussylvestris)
Shipunov BIOL 154.7
Anatomy of stem: secondary structureAnatomy of mature stemStructure of wood
Tyloses
Tyloses control the winter functioning of vessels
Shipunov BIOL 154.7
Anatomy of stem: secondary structureAnatomy of mature stemStructure of wood
Summary
Bark consists of secondary phloem and corkWood is a secondary xylemInterleaving early- and latewood form annual ringsHeartwood is a non-functioning xylem
Shipunov BIOL 154.7
Appendix For Further Reading
For Further Reading
Th. L. Rost, M. G. Barbour, C. R. Stocking, T. M. Murphy.Plant Biology. 2nd edition.Thomson Brooks/Cole, 2006.Chapter 5.3.
Shipunov BIOL 154.7
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