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Chapter 8 (Vascular Cambium (when a fusiform initial undergoes longitudial…
Chapter 8
Vascular Cambium
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in a woody species, the cells never go under cell cycle arrest
the continue to divide instead of maturing, then they constitute the fascicular cambuim
mature parenchyma cells between vascular bundles come out of cell cycle arrect and resume mitosys forming an interfasicular cambuim
Although a vascular cambium shares many features with an apical meriste, it is unique in certain aspects.
it is a simple meristem in that it only has two types of cells, fusiform initials and ray initials
when a fusiform initial undergoes longitudial cell division with a wall parallel to the circumference of the cambium (a periclinal wall
vascular cambium cells must occasionally divide longitudinally by anticlinal walls (perpendicular to the cambium surface
Ray initials are similar to fusiforms initials except they are more cuboidal #
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fusiform initials may occur in regular horizontal rows( a storied cambium) or irregularly (nonstoried cambium
a single tree or shrub has only a single vascular cambium, in the form of a cylinder, one cell thick #
secondary Xylem
all cells formed to the interior of the vascular cambium develop into secondary xylem also known as wood
an axial system is derived from the fusiform initials and the radial system is derived from the ray initials #
the axial system always contains tracheary elements, which carry out longitudinal conduction of water through wood
the radial system of xylem is usually simple. in woody angiosperms, it contains only parenchyma
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most important angiosperm woods contain large amounts of fibers, making them strong, tough, and useful for construction . they are called hardwood
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the first wood formed is called the early wood, also called the spring wood #
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within a cross section of wood you can see where the two come together which makes up one year of growth called an annual ring
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outer bark
contribute to the larger diameter of the stem or root and increase the pressure acting on the outer tissue #
parenchyma cell activate during the formation of interfascicular vascular tissue but in secondary phloem
this results in a new cambium, the cork cambium also called the phellogen
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