Consists of three parts:

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LEAF
Consists of three parts Epidermis, mesophyll
and vascular bundles

• Epidermis
• A single layered cells covering the leaf
  surface.
• Consists of the upper epidermis and lower
  epidermis

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• Cells in the upper epidermis do not contain
• chloroplasts except in the guard cells.

• The main function of the epidermis is to protect
  
• tissues in the inner part of the leaf.

• Cuticle is found on the surface of epidermal
  cells,
• including wax

• In some plants, crystals (a form of waste
  material)
• are found in the epidermal cells.

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• Various forms of glands may be found in the
• epidermis.

• Generally, the lower epidermis is similar to
  the upper
• epidermis, except that the lower epidermis
  has
• more stomata.

• Some plants possess stomata only in the lower
• epidermis, while in some plants stomata are
  found
• only in the upper epidermis e.g. aquatic
  plants

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Epidermal surface of a leaf
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• There are two guard cells around the stomatal
  pore.
• The guard cells are normally smaller than
  the
• surrounding epidermal cells and contain
  chloroplasts.

• The function of stomata is to regulate the
  exchange of
• gas between the inner part of leaf and the
  atmosphere,
• as well as the evaporation of water that
  enters the plant
• through the roots.

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Mesophyll

• The part which lies between the upper and lower
  epidermis.
• Mesophyll cells contain numerous
  chloroplasts.
• Photosynthesis occurs mainly in the mesophyll
  tissue.

• The mesophyll tissue usually are of two parts

i) Palisade mesophyll which usually consists
of two layers of elongated parenchyma cells that
are closely packed in a vertical manner.
ii) Below is the spongy mesophyll that consists
of irregular shaped parenchyma cells that
are loosely packed, with abundant air
spaces between them to allow more
efficient air exchange.
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Vascular bundles

• Form the midrib and veins of various sizes in
  the
• mesophyll. Consist of xylem and phloem
  tissues and
• surrounded by thick walled parenchyma cells
  termed
• the bundle sheath
• The phloem transports carbohydrate manufactured
  by
• mesophyll cells to all parts of the plant,
  while water
• from the root is transported by the xylem
  to the leaf.

• In monocot leaves, the mesophyll is often not
• distinguished into the palisade and spongy
  layers.

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• In some monocots, e.g. in the Gramineae, there
  are
• large cells with thin cell walls found on
  both sides of
• the midrib, usually in the upper epidermis,
  called
• bulliform cells.
• Under dry condition, the bulliform cells
  shrink,
• causing the leaf to roll, thus help reduce
  the rate of
• transpiration from the leaf.

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