Chapter 6: Anatomy of Flowering Plants

The location and function of different types of meristems are as follows:

Yes, cork cambium forms tissues that, in turn, form the cork. When the stem increases in girth, another meristematic tissue known as phellogen or cork cambium grows in the cortex region of the stem. This phellogen cuts off cells on both sides. The outer cells differentiate into the phellem or the cork, while the inner cells differentiate into the phelloderm or secondary cortex. The cork is impermeable to water because of suberin, rendering protection to the tissues underneath.

The primary xylem and phloem exhibit the presence of a strip of cambium in woody dicot roots known as the interfascicular cambium, which is formed from the cells of the medullary rays connecting the interfascicular cambium. Hence, the continuous cambium ring is formed. The cambium separates from the newly formed cells on either side, while the cells found towards the exterior differentiate into the secondary phloem. The cells detach towards the pith giving rise to the secondary xylem. The secondary xylem is synthesised in excess compared to the secondary phloem.

When there is secondary growth in plants, the girth of the plants increases, along with an increase in the water content and nutrients in order to assist the ever-growing leaves, rendering support to the plants.

(a) Monocot root and Dicot root

Monocot root

Dicot root

(b) Monocot stem and Dicot stem

Monocot stem

Dicot stem

The following characteristics can be used to distinguish if it is a monocot or a dicot stem:

Monocot stem

Dicot stem

The traverse section is of Monocot stem. It is because the vascular bundles are dispersed in monocot stems. The phloem parenchyma is not found.

Xylem and Phloem are called complex tissues because they are made of more than one type of cells which work together as a unit to perform the function. Xylem transports water, while phloem transports food.

Stomata are structures present in the epidermis of leaves. Stomata regulate the process of transpiration and gaseous exchange. Each stoma is composed of two bean-shaped cells known as guard cells which enclose the stomatal pores.

Guard cells are dumbbell-shaped, where their outer wall is thin, and the inner wall is highly thickened. These structures possess chloroplasts and regulate the closing and opening of the stomata. The epidermal cells near the guard cells, in some cases, become specialised in their structure, shape and size; they are referred to as subsidiary cells. The guard cells, the stomatal aperture and girdling subsidiary cells are collectively referred to as the stomatal apparatus.

Following are the three basic tissue systems in flowering plants:

Epidermal tissue system

The epidermal tissue system includes the epidermis and epidermal appendages. The epidermis comprises epidermal cells and guard cells, while the epidermal appendages include root hair, stem hair, stinging hair and glandular hair.

The ground tissue system

The ground tissue system is made up of simple tissues such as parenchyma, collenchyma and sclerenchyma.

Vascular tissue system

The vascular tissue system consists of complex tissues such as Xylem, phloem and vascular cambium.

The study of plant anatomy is useful to us in the following ways:

• To understand structural adaptations in plants to different climatic conditions.
• Helpful in identifying monocots, dicots and gymnosperms.
• Physiological conditions can be studied, which helps in crop improvement.
• The study of plant fibres, such as flax, jute, etc., helps in their commercial exploitation, as it enables the prediction of the strength of wood which can be utilised to its potential.