Primary internal structure of root, stem and leaves

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Primary internal structure of root:-
Zones of a typical root:- Any underground root consists of 4 parts:-
i. Apical Meristem:- It is responsible for primary growth i.e. increase in length.
ii. Elongation Zone:- The cells become permanent and elongate.
iii. Hairy Zone:- The cells differentiate and root hairs emerge. These root hairs act as tiny osmotic apparatus.
iv. Maturation Zone:- Secondary growth is occurring or has occurred. This zone works for fixation by supporting the aerial system. This zone is found only in dicot roots. It is absent in monocot roots.
Embryonic origin:- The primary aerial system of plants develops from the plumule of the embryo while the primary root system develops from the radicle of the embryo.
In dicot plants, this primary root develops into tap root. Whereas in monocot plants, this primary root is reduced or less developed. That's why monocot plants develop fibrous root system from the base part of the stem to support the aerial system and for water absorption, which is called adventitious root system.
Thus there are 2 types of roots in plants:-
i. Tap root:- A root that develops from the radicle of the embryo. Example:- Gymnosperm and dicot plant
ii. Adventitious root:- A root that develops from any part of the embryo other than the radicle. Example: - Pteridophytes and monocot plants
Primary dicot root:- 
> The exodermis is made of parenchyma.
> In this, 2-6 groups of xylem are found. That is, Diarch to Hexarch condition is found.
> In this the pith is less developed or absent.
Transverse section of ideal dicot root
(Outline diagram)
Transverse section of ideal dicot root
(Cellular diagram)
Important points:-
> In the aerial root of Tinospora, chloroplasts develop in the cells of the general cortex, that is, it is a chlorenchyma.
> The root of Morus and Salix and the prop root of Banyan tree the pericycle is multilayered.
> Homoarchic Root:- Generally only one type of archic condition Diarch or Triarch or Tetrarch or Pentarch or Hexarch is found in the root of a plant.
> Heteroarchic Root:- In some dicots, more than one archic conditions are found in the roots of the same plant. Example:- Enhydra fluctans (Diarch, Triarch and Tetrarch three conditions are found in its root.)
Primary monocot root:- 
> The exodermis is made of sclerenchyma.
> In this, more than 6 groups of xylem are found. That is, Polyarch condition is found.
> The pith is well developed.

Transverse section of ideal monocot root
(Outline diagram)
Transverse section of ideal monocot root
(Cellular diagram)
Important points:-
> In the hygroscopic root of the orchid, velamen tissue is found between the epidermis and exodermis, which helps in absorbing water vapor from the atmosphere. In addition to this, air chambers are found in the general cortex which provide tensile strength to this root.
> Less developed root system:- If root hairs are absent in a root, it is considered to be less developed. It is an ecological adaptation of hydrophytes. Example:- Eichhornia (Hyacinth)
> Pectin is found in the cell wall of root hairs. This pectin combines with water to form a sticky substance that binds the root hairs to the soil. That's why when we uproot a plant along with its root system, soil sticks to its roots.

Primary internal structure of stem:-
Primary dicot stem:- 
> The hypodermis is made up of collenchyma.
> The ground tissue is differentiated into general cortex and endodermis.
> Eusteel is found here.
> The pericycle is heterogenous which is made up of parenchyma and sclerenchyma.
> Pith is found in the center.
Transverse section of ideal dicot stem
(Outline diagram)
Transverse section of ideal dicot stem
(Cellular diagram)
Cucurbita stem:- The following differences are found in this stem -
i. 5 ridges and 5 grooves are found on the stem.
ii. The hypodermis is found only in the ridges.
iii. The general cortex is composed of chlorenchyma, which carries out gaseous exchange through stomata located in the grooves.
iv. The endodermis is wavy, which is also called the starch sheath.
v. The pericycle is homogenous and is made up of sclerenchyma.
vi. Vascular bundles are not attached with the pericycle but are found in 2 rings of 5 and 5. In the outer ring small vascular bundles are arranged below the ridges. Large vascular bundles are in the inner ring arranged below the grooves.
vii. Instead of the pith, a large pith cavity is found in the center.
Transverse section of Cucurbita stem
(Outline drawing)
Primary monocot stem:- 
> The endodermis is made up of sclerenchyma.
> The ground tissue is undifferentiated.
> Individual bundle sheath is found around each vascular bundle.
> Atactosteel is found here. Vascular bundles are scattered in the ground tissue.
> The pericycle is absent here.
> Pith is absent here.
Transverse section of ideal monocot stem
(Outline diagram)
Transverse section of ideal monocot stem
(Cellular diagram)
Important points:-
> In the monocot stem, hairs are found initially, but later they are destroyed. But on the stem of maize, hairs are absent from the starting.
> Shining:- In some monocot plants, the stem give shining when exposed to light. It is an xerophytic adaptation.
> In maize, small vascular bundles are found on the outside and large vascular bundles are found on the inside.
> The shape of the xylem in monocot stems can be of two types:-
i. Y - shaped:- When the lysigenous cavity is absent. Example:- Wheat
ii. V - shaped:- When a lysigenous cavity is present. Example:- Maize

Primary internal structure of leaf:-
Symmetry:- Due to flattened, the leaf has bilateral symmetry. While stem and root are cylindrical, they have radial symmetry.
Types:- There are 2 types of leaves found in plants -
i. Dorsi-ventral leaf:- A leaf whose both surfaces are completely differentiated. The dorsal surface is light green while the ventral surface is dark green. Reticulate venation is found here. Example:- Dicot leaves
ii. Isobilateral leaf:- A leaf whose both surfaces are undifferentiated. Both the dorsal surface and the ventral surface are of uniform green colour. Parallel venation is found here. Example:- Monocot leaves
Dicot leaf:- 
> The hypodermis is made up of collenchyma, which is found only in veins.
> Leaf mesophyll is differentiated into - pallisade tissue and spongy tissue
> Stomata are found only on the dorsal surface.
> Xylem is found towards the ventral surface and phloem is found towards the dorsal surface.
> Protoxylem is always towards the upper surface and metaxylem is always towards the lower surface. This arrangement is called Endarch.
Transverse section of ideal dicot leaf
(Outline diagram)
Transverse section of ideal dicot leaf
(Cellular diagram)
Important points:-
> The pallisade tissue can also be bilayered. In such a situation, the upper surface is more dark green.
> Ficus has layers of pallisade tissue on both the surfaces.
> In Eucalyptus the leaf mesophyll is made up of pallisade tissue only.
> In Thymalea the pallisade tissue is found towards the lower surface.
> In Calotropis the xylem is crescent shaped.
> The lower epidermis is removed for microscopic examination of stomata. It is easy to remove because the cells of the spongy tissue found on this side are loosely arranged.
Monocot leaf:- 
> The hypodermis is made up of sclerenchyma which is found only in veins.
> Mesophyll is undifferentiated - spongy tissue
> Stomata are found on both the dorsal and ventral surfaces.
> Xylem is found towards the ventral surface and phloem is found towards the dorsal surface.
> Protoxylem is always towards the upper surface and metaxylem is always towards the lower surface. This arrangement is called Endarch.
Transverse section of ideal monocot leaf
(Outline diagram)
Transverse section of ideal monocot leaf
(Cellular diagram)
Note:- Unifacial leaves are found in onion.