Transcript Longitudinal Parenchyma

Hardwood Anatomical Structure
• Longitudinal Cells
• Ray Tissue
• Distinction from Softwood
anatomy
• Identifying characteristics
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Longitudinal Cells
• Fibers
• Vessel Elements
•Longitudinal Parenchyma
• Tracheids
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Fibers
Fiber Tracheids – long, tapered, thick walled
hardwood xylem cells
Similar to Softwood Tracheids:
• Contain bordered pits
• Secondary thickening of cell wall
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Fibers
Distinction from Softwood Tracheids:
• Shorter in length, 1 – 2 mm
• Round in cross section
• Almost solely responsible for strength
Libriform fibers – Similar to fiber tracheids
except for “apparent simple pits”
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Vessel Elements
Vessel Elements – Specialized vertical conducting cells
• Much larger in diameter than other longitudinal
hardwood cells
• When viewed in cross section commonly
termed pores
• Typically they do not elongate
• These cells join vertically to form vessels
• Vessels often stray from straight alignment
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Vessel Elements
Wide range of pore diameters 20 – 300 µm
Variation often occurs within a growth ring:
Ring Porous – Early wood contains large vessels
late wood with smaller pores
Diffuse Porous – Fairly uniform pore diameter
throughout growth rings
Semi–ring–porous or semi–diffuse–porous
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Vessel Elements
Perforation Plates: Cell divisions that contain unrestricted
voids or perforations that allow fluid transport
Perforations formed by enzymatic degradation of plates upon
maturation of the cells
Perforation plate patterns can
be use for species identification
purposes
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Vessel Elements
Vessel Pitting:
Vessel to Vessel – Three typical arrangements (below)
Vessel to fibers or tracheids – Typically bordered
Vessels to parenchyma – Bordered, half-bordered, or simple
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Vessel Elements
Tyloses: Outgrowths (or ingrowths!)
of parenchyma cell walls into the lumen
of adjacent vessel elements
Function: Primarily in damaged tissue
• Protect against moisture loss
• Prevent the spread of pathogens
• Act as a barrier in the formation
of heartwood
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Vessel Elements
Tyloses formation:
Enzymatic degradation of pit membranes between
parenchyma and vessel elements
Outgrowth of parenchyma cell membrane into vessel (Tylosis)
Tyloses may remain thin walled or experience secondary
thickening
Presence of tyloses can affect the utilization of wood
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Longitudinal Parenchyma
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Parenchyma are thin-walled storage
cells
May have darkly-stained contents
May comprise 1-24% of wood volume
(domestic hardwoods); may be up to
50% (some tropical species)
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Longitudinal Parenchyma
Axial strand parenchyma – formed by transverse division
of fusiform cambial initial
Fusiform parenchyma – derived from fusiform cambial initial
tapered at both ends, storied
arrangement
Epithelial cells – surround gum canals or gum ducts,
typically traumatic in origin
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Longitudinal Parenchyma
Parenchyma
Arrangement:
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Hardwood Rays
Cell Types – Ray Parenchyma
Procumbent – horizontally oriented when viewed in radial plane
• procumbent = “lying down”
• rectangular cells in brick-like arrangement
• typically found at the center of rays
Upright – vertically oriented when viewed in radial plane
• sometimes called square ray cells
• long axis of cell aligned vertically
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Hardwood Rays
Ray types:
Homocellular – composed of a single
cell type; either procumbent or upright
Heterocellular – composed of both procumbent
and upright ray parenchyma cells
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Rays may be narrow (uniseriate), multiseriate,
wide “oak-type” (very wide multiseriate rays)
or aggregate
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