ANATOMY OF FLOWERING PLANTS

Anatomy of flowering plants:

Introduction:

Anatomy is the study of internal structural organization. Plant anatomy includes organization and structure of tissue. A group of cells with common origin is called tissue. Cells of tissue usually perform common functions. Tissues are of following two types:

1)      Meristmatic tissue

2)      Permanent tissue

Meristmatic tissue:

Ø  These cells have the capability to divide are isodiametric in shape.

Ø  This tissue contains immature and young cells which are capable of repeated division.

Ø   There is no intercellular space is found.

Ø  They contain homogenous thin wall.

Ø  They contain large nuclei associated with abundant cytoplasm.

Ø  Meristmatic tissue is metabolically very active but they do not contain stored food material.

Ø  It is found in growth regions of plants. Eg: Root tip, shoot tip, buds etc.  Meritmatic tissues are further divided into two types:

Primary Meristmatic tissue:

It appears early in the life of a plant, which are responsible for formation of primary plant body. It further subdivided into two types:

a)      Apical meristem: It is found at the apex of root and stem during the formation of leaves and elongation of stem, some cells are left behind from shoot tip. These cells constitute the axillary bud.  Axillary buds are present in the axil of leaves. It is capable of forming a branch of flower.

b)      Intercalary meristem: It is found between mature tissues in grasses.  This tissue helps in regenerating parts which were removed by grazing animals.

Permanent tissue: Plant cells that were newly formed become specialized and lose the ability of the cell to divide and have attained a permanent shape, size and function due to the division and differentiation in meristmatic tissues. Cells of this tissue are either living or dead, thin walled or thick walled. Such cells are called permanent or mature cells and later form the permanent tissue. These tissues are derived from meristmatic tissue. There are two types of permanent tissue:

a)      Simple tissue: This tissue is called simple tissue because all the cells present in this tissue are alike or of same type. Simple tissue are of following three types:

a)      Parenchyma: Cells are usually isodiametric. They can be spherical, oval, round, polygonal and elongated in shape. The cell wall thin and made up of cellulose. Cells of parenchyma are closely packed or have small intercellular spaces. Main function of parenchymatous cells is photosynthesis, storage and secretion. This cell constitutes most part of the plant.

b)      Collenchyma: Name coolenchyma coined by Schleiden (1839). These cells are thickened at corners due to the deposition of cellulose, hemicelluloses and pectin. Cells can be oval, spherical, and polygonal. Collenchyma is present in layers below epidermis in dicot plants. They contain chloroplasts. No intercellular space is found. It provides mechanical support to growing part of the plant such as young stem and petiole of leaf and also provides flexibility to plant.

c)        Sclerenchyma: These cells were discovererd and coined by Mettenius (1805). Cells are long, narrow and have thick lignified cell wall. There can be narrow or few pits in sclerenchyma. Cells are usually dead due to the absence of protoplasm. They can be either fibres or sclerides. Fibres are thick walled elongated and pointed cells. Fibres generally occur in group in various parts of plants.  Sclerides are spherical, oval or cylindrical cells. They have highly thickened dead cells with very narrow lumen. Sclerenchyma are usually found in the walls of nuts, pulp of fruits like guava, pear and acrus sapota, seed coat of legumes and leaves of tea. Its main fuction is to provide mechanical support.

Complex tissue:

It is made up of more than one type of cells. They work together as a unit. Complex tissue is of two types:

a)      Xylem: It is the water conducting tissue which helps in transportation of water and minerals from roots to whole plant. Vascular bundles are arranged in rings. It is composed of four elements:

Ø  Tracheids: They are elongated or tube like cells. They have thick and lignified walls and tapering ends. The tracheids cells are dead and protoplasm is absent.

Ø  Vessels: These are long and cylindrical tube like structure. These are made up of many cells which are called vessel members. They are interconnected through preparation in their common walls. Presence of vessels is characterstic feature of angiosperm.

Ø  Xylem fibres: They hve highly thickened walls and oblitered central lumen. Septa may be present or absent in xylem fibres.

Ø  Xylem Parenchyma: It is composed of living cells which are thin walled. The cell wall of xylem parenchyma made up of cellulose. It stores food in the form of fat or starch or tannin. Parenchymatous cells facilitate the radial conduction of water in plants.

Primay xylem consists of two types: Protoxylem and Metaxylem. Protoxylem is the first formed primary xylem element. Metaxylem is the xylem that is formed later. 

Endarch is the condition in which protoxylem lies towards the pith and metaxylem lies towards the periphery. Endarch condition is found in stem.  In Exarch condition protoxylem lies towards the periphery and metaxylem lies towards the pith. It is generally found in roots.

 

Function of xylem:

·         Helps in the transportation of water and minerals from roots to different parts of the plant.

·         It provides mechanical strength to plant.

·         It dissolve the mineral salts and sometimes fluid upward through stems.

Phloem: Phloem is the food conducting tissue in plants. It is found in angiosperms. It consists of four elements:

         i.            Sieve tube: They are long, tube like structure which are arranged longitudinally. The end wall of sieve tube perforated to form sieve plates. A mature sieve element has peripheral cytoplasm and a large vacuole but there is no nucleus. The nucleus of companion cell controls the function of sieve element.

       ii.            Companion cells: These are specialized parenchymatous cells that are closely associated with sieve tube element. There is a common pit field in the common longitudinal wall between sieve tube elements and companion cell. This pith connects both of them. Companion cells help in maintaining the pressure gradient in the sieve tube.

      iii.            Phloem parenchyma: Cells of phloem are elongated, cylindrical with tapering ends. Cells have dense cytoplasm and nucleus. The cell wall is composed of cellulose and has pits. Plasmodesmata connections exist between cells through these pits. It can store food and other substance like resin, latex and mucilage. It is usually absent in monocots.

     iv.            Phloem fiber: It is also called Bast fibers. They are made up of sclerenchyma. It is usually absent in primary phloem but present in secondary phloem. They are much elongated, unbranched and have pointed, needle like apices. Phloem fibers of jute, flax and hemp are commercially used.

Protophloem is the condition in which primary phloem formed firstly. It consists of narrow sieve tube.

In metaphloem condition secondary phloem firstly and has bigger sieve tube.

 

Anatomy of Leaf:

Dorsiventral Leaf (dicot leaf):

Ø  Stomata are absent or less abundant on the upper side of leaf or upper epidermis (adaxial). Widely spreaded on lower epidermis (abaxial).

Ø  Mesophyll is differentiated into two parts: upper palisade parenchyma and lower spongy parenchyma.

Ø  Bundle sheath is single layered and formed of colourless cells.

Ø  Hypodermis of the mid rib region is collenchymatous.

Ø  Vascular bundles are present in veins and midrib.

 

Isobilateral Leaf (monocot leaf):

Ø  There is no spongy parenchyma.

Ø  Stomata are equally distributed on both side of leaf.

Ø  Bulliform cells are present with parallel venation.

Ø  Mesophyll is undifferentiated.

Ø  Bundle sheath may be double or single layered.

Ø   Hypodermis of the mid rib region is sclerenchymatous.

Anatomy of dicot and monocot plants:

Dicot roots:

Ø  In epidermis region root hairs are present on the cortex.

Ø  In endodermis region casparian strips are present which are made up of suberin layer.

Ø  Pith is small.

Ø  Conjuctive tissues are present between xylem and phloem.

Ø  Cambium ring is present which consists of 2-4 xylem and phloem.

Ø  Stele also present which includes endodermis, pericycle, vascular bundles and pith.

Monocot roots:

Ø  No cambium in the vascular bundles. Six vascular bundles are scattered which are called polyarch.

Ø  Pith is large.

Ø  No cambium and no secondary growth.

Dicot stem:

Ø  Epidermis, cuticle, trichomes, hypodermis are there with collenchymas.

Ø  Cortical layer made up of parenchymatous cells

Ø  Vascular bundles are present in rings.

Ø  Conjoint, open and endarch protoxylem.

Ø  In pericycle vascular bundles or medullary rays are present.

Ø  Pith is larger and includes parenchyma.

Monocot stem:

Ø  Epidermis-hypodermis (sclerernchyma) vascular bundles are scattered.

Ø  Vascular bundles are conjoint or closed.

Ø  No secondary growth is there.

Ø  No trichomes.

 

 

SEED:

Seed is developed from ovules inside the ovary after fertilization. A seed is generally made up of seed coat and enclosed inner parts like cotyledons, plumule and radicle. The cotyledons stores reserve food which is to be used during resting period and also helps in germination. The plumule give rise to shoot and the radicle give rise to root system. On the basis of number of cotyledons, seeds are divided into two types: Monocot seeds and Dicot seeds. On the basis of presence or absence of endosperm dicot seeds are of two types: endospermic seed and non-endospermic seeds.

Dicot seed:

The endospermic seeds of castor and custard apple controls an outer hard, blackish and mottled shell called testa or seed coat. There is an outgrowth at the micropyle called caruncle, which is spongy and absorbs moisture readily during seed germination. A ridge called raphe, formed by the funicle. The perisperm, a remnant of nuclleus and thin watery papery membrane surrounding endosperm. Endosperm, a fleshy food storage tissue, rich in oil is present under the cover of perisperm. Embryo lies embedded inside endosperm, and contain two thin cotyledons hinged to an axis called tigellum. Tigellum shows a protruding radicle and the plumule hidden between cotyledons. The non- endospermic seeds of gram, pea, and bean are also covered by a seed coat. The seed coat is generally two layered: Outer one is called testa, and inner tegmen. Hilum is the point of attachment of seed with the stalk. A minute opening (micropyle) above the hilum of an outgrowth (raphe) are also distinct. The embryo consists of an axis (tigellum) and two fleshy cotyledons full of reserve food material. The lower pointed end of the axis is radicle and the upper leaf end is called plumule.

Monocot seeds:

Monocot seeds are with single cotyledons and are greatly endospermic. Seed coat is membranous and fused with the fruit wall. The mainlook of the grain is endospermic which stores food. Endosperm is separated from the embryo by a distinct layer called as aleurone layer. The embryo is small and occurs in groove at one end of the endosperm. It consists of one shield shaped cotyledon called as scutellum, a short axis with plumule and radicle. The plumule is covered by a sheath called coeloptile. The radicle is protected by coeloptile. Similarly, the radicle is protected by coleorhiza. Some monocots are non-endospermic. Eg: Orchid, Saggitaria.

Seeds are the dispersal and propagation units of most plants. There are three basic parts of a seed in the angiosperm:

         i.            Embryo

       ii.            Endosperm, a food storage or nutritive tissue

      iii.            Seed covering or seed coat

Seed coat (Testa):

A tough, hard coat, the testa protects the seed from fungi, bacteria and insects. It has to be split open by the radicle before germination can proceed. The testa also has two anatomical features that might be a little harder to identify. The hilum is a scar left by stalk which attaches the ovule to the ovary wall. The micropyle is a tiny pore in the testa opposite to the tip of radicle. It supplies water to the embryo before active germination.

Plumule is the embryonic shut. In it two or more leaves are usually visible with a growing pit enclosed between them.

Hypocotyl is the part of the plant embryo or seedling plant i.e. between the cotyledons and the radicle or root. In a seedling it is the sprout structure above ground that supports the cotyledons.

Function of Seed:

·         Primary function of seeds is reproduction in which plants perpetuate themselves, mainly sexually.

·         Seed is widely used in the deliberate production of seedlings called as plant propagation.

·         Seeds protect young plants while they are being moved to a new location. They also id in the growth of new plant by providing nutrients until it is established enough to grow on its own.

·         Some seeds also attract animals that help move the seeds or have adaptations that aid in there dispersal by wind or water.

·         Some seeds also prevent the embryo from growing until environment is suitable for plant growth.

·         Most seeds are not dormant, but in a quiescent state, needing water and the right temperature for cellular growth.

 

FRUIT:

·         Fruit is the mature or ripened ovary. In fleshy fruits, the outer layer(which is often edible) is pericarp, which develops from the ovary wall of flower and surrounds the seed but in some pericarp fruits, the edible portion is not derived from the ovary.

·         Eg: In the fruit of the ackee tree the edible portion is an aril and in the pineapple several tissue from the flower and stem are involved. The outer covering of the seed is tough because the parent plant needs to protect the plant growth.

·         Fruits are categorized into three types:

a)      Simple fruit: Fruits are formed from single ovary and may contain one or many seeds. They can be either fleshy or dry. Eg: Berries, drupes.

b)      Aggregate fruit:  These types of fruit formed from single compound flower and contain many ovaries. Eg: Raspberries, Blackberries.

c)       Multiple fruit: Multiple fruits are formed from fused ovaries of multiple flowers.     Eg: Pineapple.

Anatomy of simple fruit:

In berries and drupes, the pericarp forms the edible tissue around seeds. In citrus Stone fruit (Prunus), only some layers of pericarp are eaten.

1.       Pericarp layer: Pericarp is made up of three layers: Epicarp, outer layer; mesocarp, middle layer; Endocarp, inner layer surrounding the ovary or the seeds in a citrus fruits, the epicarp and mesocarp make up the peel.

Ø  Epicarp: It is derived from greek word epi-on or upon and carp- fruit. It is the outermost layer of the pericarp. Epicarp forms the tough, outer skin of the fruit, if there is one. Epicarp also called as exocarp especially in citrus.

Ø  Mesocarp: It is derived from greek word meso- middle, carp-fruit. It is the fleshy middle layer of the pericarp of a fruit. It is found between the epicarp and endocarp. It is usually the part of fruit that is eaten.

Eg: Mesocarp makes up most of the edible part of a peach and considerable part of tomato.

Ø  Endocarp: It is derived from the greek word endo- inside, carp-fruit. It is the innermost layer of the pericarp which directly surrounds the seed. It may be membranous as in citrus, where it is the only part consumed or thick and hard as in the stone fruit of the family Rosaceae such as peaches, cherries, plums, walnuts etc. and it is removed prior to consumption.

Function of Fruit:

         i.            Fruits aid in the protection of seeds. The fruit serves as a physical barrier between the seeds and the external environment during seed development. The developing fruit (ovary) promotes ovule or seed development by preventing dessication and ensuring moist environment for embryo. In some species, fruits cause seed dormancy or prevent premature germination.

       ii.            Fruits aids in the dispersal of mature seeds.

Eg: Coconut nuts floats in water and are thus transported to distant places.

       Birds eat the seeds and pook out seeds far away and also if the fruit falls to the ground (with seed inside) fruit contain nutrients for seed to grow.

      iii.            Fruits help in plant propagation. In angiosperm both fruits and seeds are formed through a process called double fertilization. Some of these fruits have been used as distinct organ in producing new plants either naturally or deliberately. With the use of such plant organ, the method of reproduction is still considered sexual.

     iv.            Fleshy colored fruits attract birds and animals and are eaten by them. They pass unharmed through the digestive tract and are thus dispersed away from parent plant.

       v.            Some fruits have hooks or spurs, which cling to the skin and fur of animals and are, dispersed too far away places.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

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MORPHOLOGY OF FLOWERING PLANTS

Plant Morphology means study of external characters or physical form of plant. Plant are characterized by root, stem, leaves, flower and fruit.They all are further modified to perform various functions.

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