Examine the root, stem and leaf tissue layers of monocotyledonous and dicotyledonous plants.

Introduction

Angiosperms, the flowering plants, are the most highly evolved plants and the most dominant in present times. The cells of angiosperms are prearranged into different tissues and organs (Curtis et al 1989). The three main organs of flowering plants are roots, stems, and leaves. All the are basically divided into two major groups or classes, the Dicots and the based on a variety of the structural appearance. Most of these features can be identified with the naked eye including, the number of seed leaves, root system, appearance of vascular bundles in stems, vein arrangement in the leaves and the number of floral parts (Blake et al 2001). While monocots and dicots are composed of the same tissues (ground, vascular and dermal tissues) the arrangement of these tissues differs (Curtis et al 1989).

The internal structure of the angiosperm root is comparatively simple (Curtis et al 1989). In dicots and most monocots, the three tissue systems (dermal, ground and vascular) are arranged in three layers: the epidermis, the cortex, and the vascular cylinder (Curtis et al 1989). The epidermis, which covers the entire surface of the root, absorbs water and minerals from the soil and protects the internal tissues (Curtis et al 1989). The epidermal cells of the root are characterized by fine, tubular outgrowths, known as root hairs (Curtis et al 1989). Most of the water and minerals that enter the root are absorbed by these root hairs (Curtis et al 1989). The second layer of the root is the cortex which occupies by far the greatest volume of the root (Curtis et al 1989). The cells of the cortex usually lack functional chloroplasts. Instead, the plastids are specialized for food storage and contain organic compounds such as starch (Curtis et al 1989). The many spaces in the cortex allow oxygen from the soil to enter through the epidermal cells (Curtis et al 1989). Unlike the rest of the cortex, the cells of the innermost layer, the endodermis, are condensed and have no spaces between them in order to regulate the passage of water and dissolved minerals (Curtis et al 1989). The third and the inner layer of the root is called the vascular cylinder. It consists of xylem and phloem surrounded by one or more layers of cells from which branch root arise (Curtis et al 1989). In most plants, the vascular tissues of the root (xylem and phloem) are grouped in a solid cylinder. However, in some monocots, the vascular tissues form a cylinder around a pith (Curtis et al 1989).

Stems display leaves to the light and the chief functions of stems are the production and support of leaves and reproductive structures, conduction of water and dissolved minerals (Blake et al 2001). They may also in some plants, have the specialized functions of storing water and manufacturing food (Blake et al 2001). The dermal tissue or the outer surface of stems is made up of epidermal cells (Blake et al 2001). Green stems are photosynthetic and are covered with a waxy cuticle that contains stomata to prevent the loss

of water by evaporation (Blake et al 2001). The arrangement of vascular bundles differs in the stems of monocots and dicots. In monocots, the vascular tissue occurs in many scattered bundles throughout the stem. In dicots, the vascular bundles are arranged in a ring; the remainder of the stem makes up the fundamental tissue and is usually divided into the cortex, the portion outside the ring of vascular bundles, and the pith, the portion inside the ring (Curtis et al 1989).

A leaf is an extension of a plant's stem. The structure of a leaf is a compromise between ...