Page 9 - LN-ANATOMY OF FLOWERING PLANT

The cells are parenchymatous and living. Each cells has a large central vacuole and
a peripheral thin cytoplasm. It is thicker in xerophytic plants. In roots the. outermost
layer called epiblema, has tubular, unicellular, projections called root hair. The other
substances deposited on cuticle surface may be oil, resin, silicon and salts (calcium
oxalate or calcium carbonate).
Stomata The stomata (sing, stoma) are openings in the epidermis of most of the
aerial parts of the plants, especially the leaves. Each stomata is composed of two
bean-shaped cells called as guard cells, which enclose stomatal pore. The guard
cells are generally much smaller in size as compared to other epidermal cells. They
are sensitive to even a small change in turgor pressure. The dimension of stomatal
pore varies from species to species but it measures about 20 Jim long and about 10-
20 p.m wide when fully open.
In some species, the guard cells are surrounded by subsidiary cells or accessory
cells which differ morphologically from the other epidermal cells. The guard cell
walls have special elastic properties. The adjoining cell walls of two guard cells
around pore are free and not attached with each other.
These properties help them to stretch laterally during stomatal opening. The
stomatal aperture, guard cells and the surrounding subsidiary cells are together
called stomatal apparatus.
In most monocots, the guard cells are dumb bell-shaped. The stomata are mostly
found on the upper epidermis of the leaves. In some hydrophytes, the stomata occur
on the upper surface to avoid water contact.
Based on their distribution, stomata are of following types
(a) Apple Type Present on the under side of a leaf, e.g., Apple, mulberry.
(b) Oat Type Stomata are almost equal on the two surfaces, e.g, Maize, oat.
(c) Potato Type These are more on the under surface, e.g, Cabbage, potato, bean.
(d) Water lily Type These stomata are more on the upper surface, e.g., Many aquatic
plants.
(e) Potamogeton Type Stomata vestigial or absent, e.g, Potamogeton.