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Pinus Classification General and Internal structure

Pinus

Division: Bryophyta

Class: Pinopsida 

Order: Finales 

Family: Pinaceae

Genus: Pinus 

Occurrence

The genus pinup has about 90 species. It has worldwide distribution .they are mostly present in the temperate regions. Four species of pinups are found in Pakistan. Pinus wallichiana, pinups halepensis, pinups roxburghii, pinups gerardiana.

General structure (vegetative structure)

The plant body is the sporophyte. It is a tall evergreen tree. The plant body is divided into three main parts, which are root, stem, and leaves. 

Stem 

The main trunk is unbranched. It has branches confined to the apical region. These branches form a characteristic canopy. It is covered with scaly bark. Its branches are dimorphic 

  • Branches of unlimited growth: the main branches have unlimited growth.
  • Branches of limited growth: These are about 1_2cm long branches of little development produced in the axil of the scale leaves on the main branches. 

Leaf 

Scale leaves and foliage leaves are present in pinus.

  • Scale leaves: small, membranous, and brownish are the character of scale leaves. These are protective in function.
  • The foliage leaves are green and needle-like. They can be found on dwarf shoots forming the spur. 

Roots:

Pinus has a well-developed taproot; it remains short and grows on hard ground or rocks. The lateral roots are well developed. These roots spread over a large area. Young roots are infested with a fungus to form mycorrhiza. 

The internal structure of the stem :

Pinus Classification General and Internal structure

The stem is differentiated internally into the epidermis, cortex, vascular tissue, and central pith. 

Epidermis :

The surface is covered by a highly cutinized below the epidermis in which a hypodermis formed layers of lignified CELLS.

Cortex: the cortex is formed of parenchymatous CELLS. Many resin canals are present in the cortex, and each resin canal is surrounded by a layer of resin secreting glandular. 

Vascular bundle :

The vascular bundles are conjoint, collateral, and open the form phloem towards the outer sides. Secondary growth takes place by the activity of the cambium RINg. 

There are distinct annual growth rings in the wood pericycle present exterior to the vascular bundle’s ring.

The internal structure of leaf:

A transverse section shows the following internal parts of the leaf:

Epidermis:

A thick-walled epidermis .epidermis cover the leaf is covered by a thick layer of cuticle sunken stomata are present below the general surface .two or three-layered hypodermis is present underneath the epidermis. The hypodermis is composed of sclerenchymatous tissues .this hypodermis is the main strengthening tissue of the leaf.

Mesophyll:

The mesophyll of the leaf is parenchymatous .it is not differentiated into palisade and spongy parenchyma.

The internal structure of the root

Piliferous layer: it is the outermost layer of the root. 

Cortex:

A few layers of thin-walled parenchymatous cells are also present in the cortex.

Endodermis:

The pericycle is surrounded by endodermis.

 Pith:

A small parenchymatous pith may be present or absent in the center. Pith is mostly present in young stems.

Vascular tissues:

Vascular tissues are present in the center of the root.