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Structure of woody plants (Growth rings (The first wood formed is early…
Structure of woody plants
Vascular Cambium
Initiation of the Vascular Cambium
One of the meristems that that produce the secondary plant body
In herbaceous species, the cell located between the metaxylem and metaphloem ultimately stop dividing and differentiate into conducting tissues.
Fascicle is an old term for bundle. Fascicular cambium continue diving ell
Interfascicular cambium that connects on each side with the fascicular cambia.
2 types of cells: fusiform and ray initials
Fusiform initials
undergo periclinal cell division
Long tapered cells
Typical lengths for fusiform initials are 140 to 462 in dicots
Ray initials
short and more or less cuboidal
they also undergo periclinal cell divisions
wood plant is a combination of primary and secondary tissues.
Epidermis, cortex, vascular bundles, pith, and leaves are derived from meristem and known as primary tissues.
In woody species, additional tissues are produced in the stem and root from other meristems, they are secondary tissues.
wood and bark contain conducting to tissues, their accumulation gives plants a greater capacity to more after and minerals upward and carbohydrates downwards.
arrangement of cambial cells
Ray initials are typically grouped together in short vertical rows only one cell wide.
Fusiform initials may occur a storied cambium or a non-storied cambium.
Ray and fusiform initials are organized in specific patterns.
Hardwood and sapwood
the center of log is almost always darker in color than the outer wood.
The dark wood is hardwood and the light, moisture, outer region is sapwood.
Tylosis: wood parenchyma cells adjacent to vessels push bubbles of protoplasm through the pits into the vessel, forming a plug
Growth rings
The first wood formed is early wood, also called spring wood.
Late wood: thickened cuticle, transpiration is less and large number of newly formed vessels.
Early and late wood making up an annual ring.
Growth ring: when summer is unusually cold, tree fail to grow and produce a ring.
diffuse porous and ring porous
Secondary xylem
Types of wood cells
all cells are formed to the interior of the vascular cambium develop into secondary xylem known as wood.
woods may contain tracheids, vessel elements, fibers, sclereids, and parenchyma.
an axial system is derived from the fusiform initials, and a radial system developed form the ray initials.
The axial system always contains tracheary elements, which carry out longitudinal conduction of water through the wood.
In may species of woody angiosperms, the axial system also contains fibers.
pines and redwoods have few or no fibers known as softwoods.
Two basic types of ray parenchyma cells are upright cells and procumbent cells.
Ray tracheids: horizontal, rectangular cells.
Reaction wood
Response to the stress caused by gravity.
Secondary phloem
Formed from vascular cambium.
lenticels and oxygen diffusion
Anomalous forms of growth
Alternative cambia produce secondary bodies that differ from the common type, their growth is called anomalous secondary growth.
Outer bark
cork and the cork cambium
cork cambia also called phellogen.
Outer cell differentiate into cork cells (Phloem).
Mature layer of parenchyma called phelloderm
All tissues outside the innermost cork cambium comprise the outer bark. All secondary phloem between the vascular cambium comprise the inner bark.
