Plant Anatomy
Father of plant anatomy - N. Free
Unit of a Plant structure - Cell
Group of cells to perform a specific function - Tissue
Tissue -
The name is given by N. Grew.
This is the group of similar and dissimilar cells.
Cells which perform a common combined functions and are similar in their origin and structure is called a tissue.
Tissue is divided into two parts.
1. Meristematic tissue -
Group of cells which can be divided continuously many times are called meristematic tissue.
Cells which developed in the form of meristematic tissue are called meristematic cells.
Meristematic cells have many specifities
A. Have high potential for cell division.
B. Han bhai amount of cytoplasm
C. Have very thin cell wall.
D. many and small molecules are present which covers very less space in the cell.
Types of meristematic cells
On the basis of their position
1. Apical meristem
B. Intercalary meristem
C. Lateral meristem
A. Apical meristem -
This meristem present at the tip / apex of plant stem and root.
this meristem develops from the promeristem so apical meristem contains primary meristem.
meristematic cells just below the apical part are called sub apical meristem.
B. Intercalary meristem -
It is present between the permanent tissue also contain primary meristem.
It is present at the mid of stem.
C. Lateral meristem -
It is present at the mature part of plant and axils of leaf.
It contains secondary meristem so it can form permanent cells.
2. Permanent tissue -
These are formed from permanent cells which are specialised for structure and function and loss the ability to divide.
During formation of primary plant body specific regions of apical meristem produce dermal tissue, ground tissue and vascular tissue
Permanent tissue are of two types
1. Simple tissue
simple tissue is made up of only one type of cells which are similar in structure and function.
Simple tissue are of three types
A. Collenchyma -
It occurs in many layers below the epidermis in dicot plants.
It is found either as a homogenous layer or in patches.
It consists of cell which armature thickened at the corner due to deposit of cellulose, hemicellulose and pectin.
The cells may be oval spectacle for polygonal and contains chloroplast.
The cells from food when they contain chloroplast.
Intercellular spaces are absent.
They provide mechanical support to the growing is part of plant such as a young stem and petiole of a leaf.
B. Parenchyma -
The cells of parenchyma generally Iso- dimetric.
They may be spiracle oval rounded polygonal or elongated in Shape.
They eighter may be closely packed or have small intercellular spaces.
The parenchyma performs various functions like photosynthesis , storage and secretion.
C. Sclernchyma -
It consist of long , narrow cells with thick and lignified cell wall.
A few or many pits may be present in lignified cell wall.
They are usually dead and without protoplast.
Scalernchyma cells may be eighter fibers or scleried.
The fibers are thick walled and enlongated , pointed cells which occurs in group in various parts of plant.
The sclerieds are spherical , oval or cylindrical , highly thickened dead cells with very narrow cavities. (lumen)
These are commonly found in fruit wall and nuts, pulp of fruits like guava seed coat of legume and leaves of tea.
Sclerenchyma provides machenical support to the organ.
2. Complex Tissue -
These tissues are made up of dissimalar permanent cells. Which perform a collective function. Eg , Xylem And Phloem.
A. Xylem -
These are a type of vascular tissue which is useful for transportation of water and minerals.
It transports water and minerals fromroot to leaves and stem.
It also provides mechanical strength to the parts of plants.
Primary Xylem Is Of Two Types -
1. Protoxylem -
It is firstly form xylem.
2. Metaxylem -
It is formed later then protoxylem.
In stem of higher plants , protoxylem towards the center and metaxylem lies towards the periphery.
This type of primary xylem is called 'endarch'.
In roots of higher plants , the protoxylem lies towards the periphery and metaxylem lies towards the center. (pitch)
This type of primary xylem is called "exarch".
Xylem Is Made Up Of 4 Types Of Cells -
1. Tracheids
2. Vessels
3. Xylem Fibre
4. Xylem Parenchyma
1. Tracheids -
These are elongated and tube like cells which have thick and lignified cell wall.
It have tapering ends are dead and without protoplasm.
The inner layer of cell wall have thickening which vary in different forms.
In flowering plants , tracheids and vessels are the main water transporting elememt.
2. Vessel -
Gymnosperms lacks vessels in their xylem.
Vessel is a long cylindrical tube like structure which made up of many cells called vessel membrane.
Vessel membranes are lignified cells and have a large central cavity.
Vessel membranes are interconnected through perforations if their common wall.
The presence of vessel is a characteristic feature of angiosperms.
3. Xylem Fiber -
They have highly thickened cell wall and obliterated central lumen.
They may eighter be septate or aseptate.
4. Xylem Parenchyma -
These cells are living and thin walled.
Cell wall are made up of cellulose.
They store food material in the form of starch or fat and other substance also as tennin.
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