Key Points

Based on structure and location, plants have three tissue systems: the epidermal tissue system for covering, the ground tissue system for bulk, and the vascular tissue system for conduction.

This system forms the outermost plant covering and includes epidermal cells, stomata for gas exchange, and epidermal appendages like unicellular root hairs and multicellular trichomes.

The stomatal apparatus consists of a stomatal pore, two guard cells that regulate its opening, and surrounding specialized subsidiary cells. Guard cells are bean-shaped in dicots and dumb-bell shaped in grasses.

All tissues except the epidermis and vascular bundles form the ground tissue. It consists of simple tissues like parenchyma, collenchyma, and sclerenchyma, found in the cortex, pericycle, and pith.

The vascular system is composed of complex tissues, xylem and phloem, which together constitute vascular bundles. Xylem transports water and minerals, while phloem transports food.

Open vascular bundles, found in dicot stems, have a layer of cambium between xylem and phloem, allowing for secondary growth. Closed bundles, found in monocots, lack cambium.

In a radial arrangement (roots), xylem and phloem alternate on different radii. In a conjoint arrangement (stems and leaves), they are situated together on the same radius.

Dicot roots typically have two to four (diarch to tetrarch) xylem and phloem patches. They possess a small or inconspicuous pith and undergo secondary growth.

Monocot roots have more than six (polyarch) xylem bundles. They have a large, well-developed pith and do not undergo secondary growth.

Dicot stems are characterized by vascular bundles arranged in a ring. These bundles are conjoint, open, and have endarch protoxylem, surrounding a central pith.

Monocot stems have numerous scattered vascular bundles that are conjoint and closed. Each bundle is surrounded by a sclerenchymatous bundle sheath, and a large parenchymatous ground tissue is present.

Dicot leaves have a mesophyll differentiated into an upper palisade parenchyma and a lower spongy parenchyma. Stomata are generally more numerous on the lower (abaxial) surface.

Monocot leaves have stomata on both surfaces and the mesophyll is not differentiated into palisade and spongy parenchyma. They exhibit parallel venation.

The endodermal cells in roots have a deposition of a water-impermeable, waxy material called suberin in the form of Casparian strips. These regulate water and mineral uptake.

In grasses, large, empty epidermal cells called bulliform cells are present along veins. They help in the inward curling of leaves during water stress to minimize water loss.