In this article we will discuss about the diagrammatic representation of plant body.
The plant kingdom is composed of a great variety of individual plants ranging from relatively simple, minute, microscopic forms to highly evolved and complex seed plants which constitute the conspicuous and dominant part of earth’s vegetation.
The body of the seed plant is highly developed and structurally specialized. There is a considerable division of labour among the organs and each type of organ is so constituted that it carries on one or more particular functions successfully.
The body of a seed plant is made-up of two fundamental parts, the root and the shoot, which live under very different conditions (Fig. 1.1 A—C). The shoot comprising the stem and its lateral appendages, such as, leaves and buds, grows upward into the air. The root is the underground part and grows downward into the soil.
The primary functions of the stem are to support the foliage leaves in the light, the conduction of water and mineral substances from the soil and the conduction of food material from the sites of its manufacture to the parts where they are required for growth or stored for future use.
Growth of the shoot occurs at the tip where a group of actively dividing cells, known as apical meristem, is present. This meristem forms leaves, axillary buds and nodes and internodes during the vegetative phase. During reproductive phase the apical meristem forms flowers.
Among lateral appendages, leaves are perhaps the most conspicuous. They, in general, are characterized by their thin and expanded form. A leaf blade ordinarily includes an upper and lower epidermis, enclosing a chlorophyllous mesophyll.
It is traversed by a network of veins. The external and internal structure of leaf provides a large surface area for photosynthesis. Leaves also evaporate a large quantity of water into the air, and this process is known as transpiration.
Growth of roots in length is governed by an apical meristem, which is sub-apical rather than truly apical, being covered by a root cap. The latter is derived from the apical meristem along with other tissues of the root.
Major functions of the root are anchorage and absorption of water and some (inorganic) mineral salts. Water absorption is facilitated by the development or root hairs which are tubular extensions of the epidermal cells of the root. They enormously enhance the area of contact between the root and soil.
From the primary meristems, which are observed on the apices of the root and shoot, complex tissues are derived which form the primary plant body. The three major tissue systems of primary plant body are epidermis, derived from the protoderm, primary vascular tissues, derived from the procambium, and cortex and pith, derived from the ground meristem.
The vascular system of plants extends throughout the root and shoot and also in the leaf in the form of veins. It is made up of xylem, which conducts water and phloem, which conducts food material. Besides conduction, the vascular system also provides mechanical support to the plant. The tissues which provide mechanical support are generally developed within xylem and phloem.
In monocotyledons and certain herbaceous dicotyledons all procambial cells differentiate into xylem and phloem but in most dicotyledons and gymnosperms a layer of procambial cells between the primary phloem and xylem persists.
This produces a new lateral meristem, the vascular cambium, which is responsible for growth in thickness by the formation of secondary vascular tissues. The vascular cambium produces secondary phloem towards the outer side and secondary xylem towards the inner side of the axis. With the development of secondary vascular tissues, the epidermis and cortex and peeled off and a tough secondary protective tissue, the periderm, evolves outside the phloem.
Therefore the primary plant body is made up of the tissues derived from the primary meristems and the secondary plant body of the tissues derived from the vascular cambium and phellogen (cork cambium).
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