Anatomy Of Flowering Plants Revision Notes

 A quick revision tool for the grip on the chapter.

1

Meristematic tissue

• A meristematic tissue is a simple tissue composed of group of similar and immature cells which can divide and form new cells.
  

2

Types of meristematic tissue

Classification based on origin and development.

1. Promeristem or primordial meristem
2. Primary meristem
3. Secondary meristem

Classification on basis of position.

1. Apical meristem
2. Intercalary meristem
3. Lateral Meristem

Classification on basis of function.

1. Protoderm meristem
2. Procambium meristem
3. Ground Meristem

Classification on basis of plane of divisions.

1. Mass meristem
2. Rib or file meristem
3. Plate meristem

3

Complex permanent tissue (conducting tissue) - Xylem

The complex tissues are made of more than one type of cells, which coordinate to perform a common function. They are of two types xylem and phloem. Xylem and phloem together make the vascular bundle in plants.
1. Xylem:

• The cells have thick cell wall and many of them are dead.
• This tissue helps in the transport of water and dissolved substances throughout the plant.
• The different components of the xylem include tracheids, vessels, xylem parenchyma and xylem fibres.

4

Complex permanent tissue (conducting tissue) - Phloem

• This tissue helps in the transport of food throughout the plant.
• The different elements of phloem include sieve tubes, companion cells and phloem parenchyma and phloem fibres.

5

Types of vascular bundles

Xylem is classified on the basis of the position of protoxylem:

• Endarch is the arrangement where protoxylem (older xylem) is inside and metaxylem (newly formed) is outside.

• Exarch xylem has metaxylem towards the centre and protoxylem is present towards the periphery.

• Mesarch has developing xylem towards both sides which leads to the formation of protoxylem in the middle and protoxylem on the both sides.

Vascular bundles are classified on the basis of arrangement of conducting tissue:

• Conjoint- In this the xylem and phloem are present on the same radius. It is majorly of two types: Collateral vascular bundle is that in which the phloem and xylem lie on the same radius, with the phloem located toward the periphery of the stem and the xylem toward the centre. In bicollateral, two cambium and two phloem are present on both sides of xylem.
• Concentric vascular tissues have one of the tissue as central core surrounded by the other.

6

Anatomy of dicot stem

The Dicot Stem contains vascular bundles arranged in a ring around the pith. Vascular bundle is conjoint, collateral, open and endarch. Stem contains two cotyledon or embryonic leaf called as dicotyledonous stem or dicot stems.

1.  Epidermis

• It is a protective outermost single layer of parenchymatous cells without intercellular spaces.
• The outer walls of the epidermal cells have a layer called cuticle and multicellular hairs (trichomes).

2.  Cortex

• Below the epidermis, cortex is differentiated into few layers of collenchyma cells that make hypodermis which gives mechanical strength to the stem.
  
• A few layers of chlorenchyma cells are present with conspicuous intercellular spaces. Some resin ducts also occur here. 
• The third zone is made up of parenchyma cells. These cells store food materials.

 3.  Endodermis: (Starch sheath)

• The cells of this layer are barrel shaped arranged compactly without intercellular spaces. 
• Due to abundant starch grains in these cells, this layer is also known as starch sheath. 
  

3.  Stele

• It consists of pericycle, vascular bundles and pith. 
  

A)  Pericycle (Bundle cap)

• Pericycle occurs between the endodermis and vascular bundles in the form of a few layers of sclerenchyma cells.

B)  Vascular bundles

• In dicot stem, vascular bundles are arranged in a ring around the pith.  
  
• Each vascular bundle is conjoint, collateral, open and endarch.

C)  Pith

• The large central portion called pith composed of parenchyma cells with intercellular spaces.  
• The extension of pith between vascular bundles are called as pith ray or medullary rays.
•  Function of the pith is storage of food.

7

Anatomy of dicot root

The transverse section of the dicot root shows the following plan of arrangement of tissues from the periphery to the centre.

1. Rhizodermis or epiblema:

• The outermost layer is made up of single layer of parenchymatous cells without intercellular spaces. Stomata and cuticle are absent. 
• Root hairs are always single celled. 

2.     Cortex:

• Cortex consists of  oval or rounded loosely arranged parenchymatous cells. 
• These cells may store food reserves.

3.     Endodermis 

• It is made up of single layer of barrel shaped parenchymatous cells.
• The radial and the inner tangential walls of endodermal cells are thickened with suberin.  These thickenings are known as casparian strips.
• But these casparian strips are absent in the endodermal cells which are located opposite to the protoxylem elements. 

4.    Stele:  All the tissues present inside endodermis comprise the stele.
     A.    Pericycle

• Pericycle is generally a single layer of parenchymatous cells found inner to the endodermis. Lateral roots originate from the pericycle. 

      B.   Vascular system

•  Vascular tissues are in radial arrangement. 
• The tissue by which xylem and phloem are separated is called conjunctive tissue.

• Xylem showes exarch and tetrarch condition . 
• Metaxylem vessels are generally polygonal in shape

5. Pith: Usually absent

8

Secondary growth in dicot stem

In dicot stem, secondary growth takes place through the following steps:

• Formation of cambium ring
• Formation of secondary vascular tissues
• Vascular rays
• Annual rings
• Sapwood and heartwood