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Structure of Woody Plants (Secondary Xylem - wood (Two different…
Structure of Woody Plants
Vascular Cambium - meristem that produces secondary plant body
Cells between metaphloem and metaxylem that continue to divide - fascicular cambium
mature parenchyma cells that start mitosis again, on either side of fascicular cambium - interfascicular cambium
Two distinct cell types
fusiform initals - undergoes longitudinal cell division with parallel wall called periclinal wall to produce 2 cells
If outer cell remains a cambium cell then the inner cell becomes secondary xylem
as these daughter cells elongate they increase the diameter of the plant
this increase is by the cambium cells that divide longitudinally by anticlinal walls
If inner cell remains a cambium cells then the outer cell becomes secondary phloem
Ray initials - short, cuboidal
if inner cell remains cambial ray initial then outer cell becomes phloem parenchyma
if the outer cell remains cambial ray initial then the inner cell becomes xylem parenchyma
produce storage parenchyma and albuminous cells in gymnosperms
Fusiform and ray initials are organized in specific patterns
ray initials are grouped in short vertical rows
one cell wide - uniseriate
two cells wide is biseriate
many cells wide - multiseriate
FIGURE 8-15
fusiform initials are in horizontal rows (a storied cambium) or without pattern (nonstoried cambium)
Secondary Xylem - wood
tracheids, vessel elements - longitudinal conduction of water through the wood
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Both tracheary elements and fibers are made from fusiform initials but sometimes can become columns of xylem parenchyma instead
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hardwoods - have a lot of fibers making them good for construction
Two different arrangement of cells
radial system - develops from ray initials
Radial Xylem Parenchyma
stores carbohydrates and conduct material over short distances
upright cells and procumbent cells
Ray is adjacent to axial - plasmodesmata
Ray adjacent to tracheid or vessel element - pits in secondary wall
axial system - derived from fusiform initials
creates Axial Xylem Parenchyma
temporary water reservoir
conifers - contain only tracheids in axial system
angiosperms - tracheids, vessel elements in axial system
TABLE 8-2
Early wood - has lots of wide vessels and tracheids. Ring porous woods.
late woods - less vessels and cuticle thickened. Diffuse porous wood.
Secondary Phloem and Outer Bark
Secondary phloem axial system - conduction up and down the stem or root, has sieve tube members and companion cells
Cork and the cork cambium
all cells are cuboidal and after division outer cell becomes cork cell
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primary cork cell walls have suberin which makes them waterproof, chemically inert and dead
inner cell becomes phelloderm and all these together are the periderm
tissues outside the innermost cork cambium are the outer bark
all secondary phloem between vascular cambium and innermost cork cambium - inner bark
Anomalous Secondary Growth - alternative types of cambium structure that produce secondary bodies
Roots of Sweet Potatoes
increased amount of storage parenchyma due to numerous vascular cambia around each vessel element or groups of them
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as potato grows it contains hundreds of vascular cambia of various ages
multiple vascular cambia helps with growth because it speeds the production of storage capacity
Included Phloem - type of secondary phloem between two bands of xylem
advantage is protection of the phloem from insects and pests due to the layers of wood
unknown function between this new included phloem and xylem
FIGURE 8-30
Unequal Activity of Vascular Cambium
in vine species 2 sectors of cambium are active while 2 other are not
these inactive cambiums become thing, flat woody ribbon
advantage has to do with flexibility
Secondary Growth in Monocots
Joshua trees and dragon trees
vascular cambium arise just outside the outermost vascular bundles only producing parenchyma cells and no conducting cells
secondary vascular bundles - parenchyma cells undergo rapid division containing xylem and phloem
outermost cells of this bundle develop fibers with thick secondary cell walls
woody because of the fibers and branching is feasible
