Anatomical structure of vegetative plants organs.
DICOT STEMS
Dicot
stems with primary growth have pith in the center, with vascular bundles
forming a distinct ring visible when the stem is viewed in cross section. The
outside of the stem is covered with an epidermis, which is covered by a
waterproof cuticle. The epidermis also may contain stomata
for gas exchange and hairs. A cortex of parenchyma cells lies between the
epidermis and vascular bundles. Cortex includes: collenchyma,
chlorenchyma and endodermis. Vascular cylinder includes: opened collateral bundles, arranged in a ring in stele. Between xylem and
phloem is cambium in bundles of stem. Pay attention to a large amount of sclerenchyma and on large rays between bundles.
Woody
dicots and many nonwoody dicots have secondary
growth originating from their lateral or secondary meristems: the vascular
cambium and the cork cambium or phellogen. The vascular cambium
forms between the xylem and phloem in the vascular bundles and connects to form
a continuous cylinder. The vascular
cambium cells divide to produce secondary xylem to the inside and secondary phloem to the outside. As
the stem increases in diameter due to production of secondary xylem and
secondary phloem, the cortex and epidermis are eventually destroyed. Before the
cortex is destroyed, a cork cambium develops there. The cork cambium divides to
produce waterproof cork cells externally and sometimes phelloderm cells
internally. Those three tissues form the periderm,
which replaces the epidermis in function. Areas of loosely-packed cells in the
periderm that function in gas exchange are called lenticels.
Secondary xylem is commercially
important as wood.
The seasonal variation in growth from the vascular cambium
is what creates yearly tree rings in temperate climates. Tree rings are the
basis of dendrochronology, which dates wooden objects
and associated artifacts. Dendroclimatology
is the use of tree rings as a record of past climates. The aerial stem of an
adult tree
is called a trunk. The dead, usually darker inner wood of a
large diameter trunk is termed the heartwood.
The outer, living wood is termed the sapwood.
In
general, plants that complete their life cycles within one
year (annuals) have green herbaceous stems. Their tissues arelargely primary,
although cambium may develop some secondary tissues. Herbaceous dicot stems
have discrete patches of xylem and phloem
called vascular bundles, which occur in a ring that separates cortex
from the pith, although in a few plants xylem and phloem are produced as continuous rings. As previously
noted, procambium produced only primary xylem and primary phloem.
Arrangement of primary tissues
in woody dicot stems is very similar to that found in herbaceous dicot stems during the early stages of growth.
As soon as the vascular cambium and
the cork cambium start functioning, however, obvious differences begin to appear, the most conspicuous of which involve the secondary
xylem, or wood.
Rhizome of dicot occur vascular and nonvascular bundle structure
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Herbacous Dicot Stem Cross Sections
The "bark" of the tree consists of
the periderm + the phloem
Gymnosperm stems
All gymnosperms
are woody plants. Their stems are similar in structure to woody dicots except
that most gymnosperms produce only tracheids
in their xylem, not the vessels found in dicots. Gymnosperm wood also often
contains resin
ducts. Woody dicots are called hardwoods, e.g. oak, maple and walnut. In
contrast, softwoods are gymnosperms, such as pine, spruce and fir.
A RHIZOME is underground modification of stem, which is formed
at perennially herbacous plants for an accumulation nutritives and vegetative reproduction. Has
the well formed stocking parenchime; mechanical and vascular tissues are
expressed poorly. In medicine use rhizome of onion, fern, valerian and other.
Anatomic structure
of leaves
Leaf – lateral vegetative organ of plants, the general
function its are photosynthesis, transpiration
A generalized
plant cell type, parenchyma cells are alive at maturity.
They function in storage, photosynthesis, and as the bulk of ground
and vascular tissues. Palisade parenchyma cells are elogated
cells located in many leaves just below the epidermal tissue. Spongy mesophyll cells occur below the one
or two layers of palisade cells. Parenchyma cells also occur withinthe xylem
and phloem of vascular bundles.
If a typical leaf is cut transversely and examined with the aid of
microscope, three regions stand out: epidermis,
mesophyll, and veins. Epidermis is a single
layer of cells covering the entire surface of leaf. Epidermis on lower
surface of blade can sometimes be distinguished from upper
epidermis by presence of stomata. The epidermis also secretes a
waxy substance called the cuticle. These layers protect the leaf from insects,
bacteria, and other pests.
The mesophyll
("middle leaf') includes the major photosynthetic tissues: palisade parenchyma (is found only in dicot beneath
the upper epidermis, may be one or more cell
layers thick, depending on plant, packed with chloroplasts; is a primary site
of PSN in dicot); spongy parenchyma (is found in both monocot and dicot, in
dicot, will be found below the palisade
layer; in both, forms large air spaces for "storage" for carbon
dioxide, oxygen and large surface area for absorption of carbon dioxide into cells, they also contain chloroplasts).
In the center we can observe veins. The veins
contain vascular tissues. Veins support the leaf and are filled
with vessels that transport food, water, and minerals to the plant.
Anatomical structures of leaves are of several types: isolateral (common for monocot and dicot plants); bifacial
(common for dicot); radial (common for gymnosperm).
A cross-section of a pine leaf sample is
composed of many cells. Transparent cells are in pith, xylem, and endodermis.
Green cells compose mesophyll tissues. Cross-sections of stomata are only found
in the edges, or epidermis. Resin canals are found on the surface of the
mesophyll tissues. The resin canals function as water pipes for leaf.
http://www.enchantedlearning.com/subjects/plants/leaf/
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Leaf Structure:
Most food production takes place in elongated cells called palisade mesophyll.
Gas exchange occurs in the air spaces between the oddly-shaped cells of the
spongy mesophyll.
