Page 10 - LN-ANATOMY OF FLOWERING PLANT

Epidermal Appendages (Outgrowths)
The epidermis of most plants often bear outgrowth known as epidermal appendages
or epidermal outgrowths. They are of following two types
(a) Trichomes The epidermal hairs present on the stem are called trichomes. These
are epidermal outgrowths present temporarily or permanently on almost all plant
parts. The trichomes can be further divided as hair, scales, colleters and water
vesicles or bladders.
(b) Emergences (Prickles) They are multicellular, stiff and sharp epidermal
outgrowths containing some inner tissues.
•They protect the pliant against excessive loss of water and grazing. They also helps
in climbing in some plants, e.g., Rose.
Epidermal tissue system serves the following important functions
(a) It provides a protective covering all over the plant parts.
(b) It helps in gas exchange through stomata and lenticles present on the surface.
(c) The presence of cuticle helps in the reduction of evaporation of water
(epidermis).
(d) The glandular trichomes excrete various useful plant products for the plant
function.
(e) In some monocot leaves, the bulliform cells help in the rolling and unrolling of
leaves. This property helps to reduce transpiration in xerophytic plants.
2. Ground Tissue System
All tissues, except epidermis and vascular bundles constitute the ground tissue
system. It mainly forms the bulk of the plant body. It’s various components are
hypodermis, cortex, endodermis, pericycle, medullary rays and pith.
i.Hypodermis This is the region situated just below the epidermis and as an outer
region of cortex. It contains of one, two or few continuous or discontinuous layers of
collenchyma (in dicots) or sclerenchyma (in monocots). It is protective and
mechanical in function.
ii.Cortex The cortex lies between epidermis and endodermis consisting of
parenchyma, collenchyma and sclerenchyma. The cortex is distinct in dicotyledons
but not in monocotyledons. The cells of cortex contain starch grains, oil, tannins and
crystals. Sometimes, cortical cells may contain chloroplasts and are called
chlorenchyma.
In hydrophytes, the cortex may be aerenchymatous (Spongy tissue with large air
spaces found between the cells of the stems and leaves of aquative plants). The
special types of cells like sclereids, resin ducts, oil glands laticifers are found in this