Download are found in the epidermal cells. Some plants possess stomata only

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
 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.
 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
Cross section of a leaf
trichomes
crystals
veins
Epidermal surface of a leaf
 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.
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.
perforations
Palisade parenchyma
A large lateral vein
Spongy mesophyll
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.
 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.
Bulliform cells (Gramineae)