Growth Rings Result from the Periodic Activity of the Vascular Cambium

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Growth Rings Result from the Periodic Activity
of the Vascular Cambium

• Periodic activity of vascular cambium produces
  growth increments.
• Growth rings- growth increments/layers in the 2?
  xylem and phloem
• Annual ring-growth layer for one season
• False annual rings-occur due to environmental
  factors causing the production of more than one
  growth ring per season.
• Early wood
• - appears light in color
• - large diameter less dense
• - wider cells and thinner walls
• Late wood
• -appears dark in color
• - more dense
• - narrow cells and thinner walls

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The Width of a Growth Ring

• Varies from year to year depending on
  environmental factors including amount of light,
  temperature, available soil water, length of the
  growing season and rainfall.
• The most influential factor is rainfall.
• ? rainfall wide growth ring
• ? rainfall narrow growth ring
• The oldest living specimen of the Bristlecone
  Pine (Pinus longaeva) 4,900 yrs old, was studied
  by dendrochronologist to determine its past
  temperature and climatic conditions per each
  season.

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?ring-porous diffuse porous?

• Ring-porous woods - the pores of the early wood
  are distinctly larger than the late wood
• diffuse-porous woods - the pores are uniform
  throughout the growth layer
• In ring porous woods most of the water is
  conducted in the outermost growth layer at speeds
  10x greater than that of the diffuse-porous
  woods.

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Heartwood

• As wood begins to age it goes through some
  changes including
• -The loss of reserve foods
• -Infiltration of the wood by
  various substances
• After these changes occur the wood becomes
  nonfunctional in conduction and storage.
• Heartwood the central, woody core of a tree, no
  longer serving for the conduction of water and
  dissolved minerals heartwood is usually denser
  and darker in color than the outer

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Sapwood

• Sapwood relatively thin, youngest, outer part
  of the woody stem of a tree, the part that
  conducts water and dissolved materials
• The proportion of sapwood to heartwood varies
  from species to species.
• thick sapwood includes maple, ash, birch
• thin sapwoods include locust catalpa, yew

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• Tyloses balloon-like outgrowths of parenchyma
  cells that partially or completely block the
  lumen of a vessel.
• when a tylosis is fully formed it plugs the
  vessel, no longer allowing the vessel to conduct
  water.
• it is used as a defense to inhibit a pathogen
  from spreading further through the xylem.

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Tension Wood

• Hardwoods such as oaks form a type of reaction
  wood called tension wood on the upper side of the
  branch.
• wood-produced by the increased activity of the
  vascular cambium developing on the upper side of
  the stem.
• -contains no lignin and lots of
  cellulose
• Once this fails to prevent the branch from
  drooping, they switch to develop more wood on the
  undersides as shown here.

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Compression Wood

• Conifers form a type of reaction wood called
  compression wood on the undersides of horizontal
  limbs.
• produced by the increased activity of the
  vascular cambium developing on the underside of
  the stem.
• - contains lignin and little cellulose
• Compression wood attempts to prevent the branch
  from drooping.
• The pith in this pine is clearly way above the
  center point on this branch indicating much more
  development under the branch than on top.
• These branches form an oval in cross section

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The strength of wood

• Determined by density and specific gravity
• Specific gravity of a substance is the ratio of
  the substance to the weight of an equal volume of
  water.
• Specific gravity oven dry weight of wood
• Weight of the displaced
• volume of water
• thick walled, narrow lumen high sp. gravity
• Thin walled, wide lumen low sp. gravity
  

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Truth About Knots

• Knots- branches that grew on the young tree that
  eventually got embedded within the growing trunk.
• The vascular cambium in the branch and the trunk
  are one in the same the branch grows continuously
  along with the trunk.
• Tight knots- during periods of cambial activity,
  new wood is added as a continuous layer over
  branch and trunk, tightly fixing the knot in the
  wood of the trunk.
• Loose knots- a dead branch that losses its bark
  and is not firmly fixed a knot not held tightly
  in place by growth, shape or position.

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Tight knot Loose knot