PLANT ANATOMY

موضوع: PLANT ANATOMY الأربعاء يوليو 20, 2011 3:57 pm

اقرأ كتاب تشريح النبات باللغة الانجليزية من النت مباشرة دون تحميل
[ندعوك للتسجيل في المنتدى أو التعريف بنفسك لمعاينة هذا الرابط]

^{PLANT ANATOMY}

^{The
science of the structure of the organized plant body learned by
dissection is called Plant Anatomy (anatomy-dissection). In general,
Plant Anatomy refers to study of internal morphology, pertaining to
different tissues. The subject of this chapter is structure of
Angiosperms, with emphasis on primary tissues.}

^{TISSUE SYSTEM}

^{Plant
body in Angiosperms is differentiated into root stem, leaf and flower.
All these parts are made up of different types of tissues containing
different cell types. A tissue is a mass of similar or dissimilar cells
performing a common function.}

^{The body of a vascular plant is composed of dermal tissue, Ground tissue and Vascular tissue.}

^{Dermal Tissue (Skin)}

^{Dermal Tissue is protective in function. Basing on its origin, it is classified into two types – Epidermis and Periderm.}

^Epidermis:^{This
is the primary surface tissue of the entire plant. Epidermal cells are
compactly and continuously arranged; the continuity is lost by the
presence of Stomatal pores or breaks in the tissue. Covering the aerial
epidermis, cutin (fatty substance) is present as an impregnation on cell
wall. The cuticle can be separated from epidermis. The epidermis may
produce unicellular or multicellular hairy outgrowths and other
appendages. Epidermis provides mechanical protection, allows gaseous
exchange through stomata, restricts transpiration with cuticle, and is
also involved in storage, photosynthesis, secretion, absorption and
perception to stimuli. Stomata are Pores, each guarded by two guard
cells, which control the size of the pore. Cells surrounding guard
cells, but differing from other epidermal cells, are called subsidiary
cells. Guard cells are kidney shaped; their cell walls are thick on the
inner surfaces. Guard cells contain many chloroplasts.}

^Periderm:^{This is formed during secondary growth replacing primary epidermis.}

^{Ground Tissue}

^{This is inner to dermal tissue and is composed of simple tissues like parenchyma.}

^{Vascular tissue}

^{Vascular
tissue consists of conducting elements – xylem and phloem. Vascular
tissue may be scattered in ground tissue or regularly arranged forming a
ring. In the latter arrangement, ground tissue is differentiated into
cortex (outer to vascular tissue) and pith (inner to vascular tissue).
The ground tissue of leaves is called mesophyll, bound by upper and
lower epidermis.}

^{TISSUE TYPES}

^{In broad sense, tissues are classified as – meristematic and permanent tissues.}

^{Meristem (Meristos – divisible)}

^{Initially
all embryonic cells of an embryo have the capacity to divide and
multiply but as the embryo develops into a plant body, this capacity for
division is restricted to certain parts of the plant body called
meristems which are active throughout the life of the plant body (unlike
that of an animal body). When meristematic cells divide, a group of the
daughter cells remain meristematic; the other daughter cells called
derivatives differentiate into various tissue elements. Before the
occurrence of any cell division, usually cells become enlarged
accompanied with addition of protoplasmic and cell wall material.}

^{Meristematic
cells are isodiametric, compactly arranged with dense cytoplasm, large
nucleus, and small vacuoles or without vacuoles. Cell walls are thin.}

^{Meristems
which occur at the apices of stem, root and other branches are called
apical meristems, which bring about primary growth of the plants, hence
also called as primary meristems. In many plants in addition to apical
meristems, lateral meristems like vascular cambium, cork cambium,
intercalary meristems are found. Lateral meristems are arranged parallel
to the sides of organs in which they occur.}

^{Intercalary Meristem:}^{This is also a primary meristem, found inserted between permanent
tissues, in the bases of internodes and leaf sheaths of grasses.
Sometimes, as in gynophore of groundnut, xylem may be present in
intercalary meristem. Wherever stem is jointed, elongation of internodes
is due to intercalary meristem. Example: Bamboos. Even prolonged growth
of leaves, flowers and fruits may be regarded as an intercalary growth.}

^{Vascular cambium and cork cambium:}^{These are referred to as secondary meristems because they produce
secondary tissues, and increase the thickness of the plant body. This
process is called secondary growth, seen in dicotyledons and
gymnosperms.}
^{Permanent or Mature Tissues}

^{Cells
derived from meristems gradually change in their structure, metabolism
and chemistry and acquire specialized characters by their various modes
of differentiation. Not all the cells totally differ from the meristems.
Some cells retain the power of division and others cannot divide. In a
strict sense only cells which have lost the power for division must be
regarded as permanent tissues, but in a broad sense, cells derived from
meristem that have acquired a special function like photosynthesis,
secretion, storage are treated as part of matured tissue. There are
different types of mature tissues. Example: Parenchyma, Collenchyma,
Sclerenchyma, Xylem and Phloem.}

^{Types of Mature Tissues}

^{Parenchyma (Para-beside, enchyma-In poured)}

^{Parenchyma
is the fundamental tissue of the plant body. It is found in every part
of the plant body like pith and cortex of stem and root, mesophyll of
leaves, flesh of fruits, floral parts and even in xylem and Phloem.
Cells have thin primary walls and polyhedral shapes. The average number
of faces of a polyhedron is 14 and is called as "tetra decahedron".
Cells are compactly arranged or more commonly spaciously arranged with
intercellular spaces as in cortex and pith. Cells possess dense
cytoplasm and are active metabolites.}

^{Generally
cells of parenchyma are involved in storage of starch, sucrose,
protein, water, phenol derivatives, many mineral substances, etc. Other
metabolisms like respiration, protein synthesis etc., are active.
Parenchymatous cells may also perform specialized functions and are
structurally modified. The following are the different types of
parenchyma.}

موضوع: رد: PLANT ANATOMY الجمعة يوليو 22, 2011 2:41 am

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موضوع: رد: PLANT ANATOMY الجمعة يوليو 22, 2011 12:28 pm

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موضوع: رد: PLANT ANATOMY السبت يوليو 23, 2011 4:39 am

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