Please enable JavaScript.
Coggle requires JavaScript to display documents.
Ch 9: Structure of Woody Plants, Screen Shot 2021-04-05 at 8.57.43 AM,…
Ch 9: Structure of Woody Plants
Primary Tissues
make up the primary plant body but in woody plants these additional tissues are produced in the stem and root from other meristems. The Vascular Cambium and Cork Cambium
The new tissues becomes wood (Secondary xylem) and bark (Secondary phloem and cork). These are the
Secondary Tissues
that make up the plants secondary body.
Because wood and
Bark
are conducting tissues, the accumulation of these gives plants a greater capacity to move water and minerals upwards and carbohydrates downwards. The number of leaves and roots that the plant can support increases, so does the photosynthetic rate.
All cells formed to the interior of the vascular cambium develop into
Secondary Xylem
known as
Wood
.
Most important angiosperm wood contain large amounts of fibers, making them strong, tough, and useful for construction. These are called
Hardwoods
.
Woods from conifers have few or no fibers and therefore have a softer consistency. These are called
Softwoods
even though in many instances some are a lot tougher than hardwoods.
The first. wood that is formed is called
Early Wood
or spring wood, and it has to have a high proportion of wide vessels. Or in conifers, wide tracheids.
The later wood produced is called
Late Wood
, or summer wood, and can have a lower proportion of vessels. These are stronger and contain numerous fibers, or in conifers, contains narrow, thick walled tracheids.
In branches or trunks that are not vertical, gravity causes a lateral stress. If this doesn't get counteracted the branch would droop and become pendent. In response to this stress most plants produce
Reaction Wood
Seeing the two of these together forms an
Annual Ring
after each year they grow. or
Growth Ring
Because the growth ring has vessels located throughout it, this is called a
Diffuse Porous
. Where species with vessels restricted mainly to early wood are
Ring porous
The center of a log is almost always darker than the outer wood, and is usually drier and more fragrant.
The dark wood is
Heartwood
and the lighter, moister outer part is called
Sapwood
. These different region exist because the vessels and tracheids cannot survive forever in water conditions.
The
Vascular Cambium
is one of the meristems that produce the secondary body. In a herbaceous these cells are located between the metaxylem and metaphloem of a vascular bundle. They ultimately stop dividing and differentiate into conducting tissues.
In a woody system these cells never undergo cell cycle arrest. They continue to divide instead of maturing, these make up the
Fascicular Cambium
Some mature parenchyma cells between vascular bundles come out of cell cycle arrest and resume mitosis, this forms the
Interfascicular Cambium
. This connects on each side with the Fascicular Cambia.
After this the Vascular Cambium is a complete cylinder. "Fascicular" and "Interfascicular" are used only while the cambium is young. After 2-3 years these become indistinguishable and are then called the Vascular Cambium
The Vascular Cambium consists of segments of distinct ages, the closer to the ground the older and those closer to the tips of the axes being younger.
Never occurs in flowers, seeds or fruits.
The Vascular Cambium only has two types of cells
Fusiform Initials
are long tapered cells. Typical lengths are 140-462 um in dicots and 700-8,700 um in conifers.
When a fusiform initial undergoes longitudinal cell division with a wall parallel to the circumference of the cambium (a
Periclinal Wall
) it produces two elongate cells. One continues to be a fusiform initial and the other differentiates into a secondary phloem or a secondary xylem.
Vascular cambium cells must occasionally divide longitudinally by
Anteclinal Walls
perpendicular to the Cambiums surface. This causes the number of cambial cells to incr
Without this the cambial cells would be stretched wider circumferentially and finally could not function.
May occur in regular horizontal rows (
Storied Cambium
) or irregularly, without any horizontal pattern, (
Nonstoried Cambium
)
The
Axial System
is derived from these. This always contains treachery elements that carry out longitudinal conduction of water through the wood. Also contains fibers that give the wood strength and flexibility.
Ray Initials
short and more or less cuboidal. These produce short cells, mostly just storage parenchyma and in gymnosperms, albuminous cells.
Typically grouped together in short vertical rows only one cell wide (uniseriate), two cells wide (biseriate) or many cells wide (Multiseriate).
The
Radial System
develops from the Ray Initials.
The radial system of xylem is usually simple. In woody angiosperms, these contain only parenchyma, arranged as uniseriate, biseriate, or multiseriate masses called
Rays
.
Store carbohydrates and other nutrients during dormant periods and conduct material over short distances within wood.
The 2 basic types of these ray cells are
Upright Cells
and
Procumbent Cells
In addition to these cells they may contain
Ray Tracheids
. These are horizontal cells that look somewhat like the ray parenchyma cells but have secondary walls, circular bordered pits, and protoplasts that degenerate quickly after the secondary wall is completed.
Wood parenchyma cells adjacent to vessels push bubbles of protoplasm through the pits into the vessel forming plugs called a
Tylosis
completely across it. This occurs repeatedly and the vessel might become filled.
Secondary phloem
is formed from the vascular cambium just as secondary xylem is. This too has an axial and a radial system.
This results in a new cambium
Cork Cambium
also called
Phellogen
.
The inner cell always remain Cork Cambium while the outer cell differentiates into a
Cork Cell
or also called a
Phellem Cell
In a few species the cork cambium may produce a cell or two to the inside that mature into a layer of parenchyma called
Phelloderm
.
These all make up the
Periderm
All tissues outside the innermost Cork Cambium comprise the
Outer Bark
. All secondary phloem between the vascular cambium and the innermost cork cambium is the
Inner Bark
Secondary Phloem located between two band of xylem is called the
Included Phloem
.
Because alternate cambia produce secondary bodies that differ from the common type, their growth is called
Anomalous Secondary Growth
Columns of some of the parenchyma cells undergo rapid division and produce narrow cells the differentiate into
Secondary Vascular Bundles
that contain both xylem and Phloem.
