Anatomical structure of vegetative plants organs.

ROOT AND MONOCOT STEM

There are two plant groups, the Monocots and the Dicots.  The distinction between these two groups is not always clear, but some general trends are outlined below:

	Monocots	Dicots
Floral Arrangement	3's	4's and 5's
Leaf Venation	Parallel	Net
Vascular bundles	Scattered	Ring
Habit	Herbaceous	Herbaceous + Woody
Roots	Fibrous	Taproot
Growth	Primary only	Primary and Secondary
Examples:	Grass, Palm, Orchid	Oaks, Roses, Sunflowers

Primary and second secondary anatomic structure of root.

In vascular plants, the root is the organ of a plant body that typically lies below the surface of the soil. But, this is not always the case, since a root can also be aerial (that is, growing above the ground) or aerating (that is, growing up above the ground or especially above water). On the other hand, a stem normally occurring below ground (see rhizome). So, it is better to define root as a part of a plant body that bears no leaves, and therefore also lacks nodes. There are also important internal structural differences between stems and roots. The two major functions of roots are 1.) absorption of water and inorganic nutrients and 2.) anchoring the plant body to the ground. They often function in storage of food. The roots of most vascular plant species enter into symbiosis with certain fungi to form mycorrhizas, and a large range of other organisms including bacteria.

Root is descending axis of plant, normally below ground. Subapical region of roots (along section) has traditionally been divided into 3 regions: zones of the cellular division, cellular elongation, and cellular maturation. Primary tissues differentiate in or distally to zone of cellular maturation. An epidermis (in root call epiblema) surrounds root, which is usually one cell thick. Epiblema covers the entire root except the root cap and usually lacks stomata. In cross section of a root we can see zones: epiblema, primary bark (cortex) and stele. Primary bark has three layers: 1)exoderma with polyangles thick-walled cells; 2) mezoderma with oval cells and air spaces; 3) endodermis with casparian strip and conductive cells. Stele consists of pericycle - one layer of thick cells and radial vascular bundle.

In monocot roots vascular bundle is polyarch, closed, and radial. In dicot roots with primary structure vascular bundle is closed, radial, and tetraarch.

Dicot roots with secondary vascular bundle structure have opened collateral vascular bundles in stele, which are arranged in circle. This anatomic structure you can see in transition region (placing between root and shoot). Between them there are wide medullary rays which are start in primary xylem and are situated in the center of a root. Dicot roots with secondary nonbundle structure have solid ring of vascular cambium, solid zone of phloem above it and solid zone of xylem below cambium. In the center there is primary xylem. Primary medullary rays stretch from it, Secondary rays are formed by cambium.

Monocot roots, interestingly, have their vascular bundles arranged in a ring. Dicot roots have their xylem in the center of the root and phloem outside the xylem. A carrot is an example of a dicot root.

Root Anatomy - Monocot Roots

Epidermis

• Dermal tissue
• Protection of the root

Cortex

• Ground tissue
• Storage of photosynthetic products
• Active in the uptake of water and minerals

Endodermis

• cylinder once cell thick that forms a boundary between the cortex and the stele
• even more distinct than dicot counterpart
• contains the casparian strip and conductive cells

Vascular Tissue

• Xylem and Phloem
• Forms a ring near center of plant

Pith

• Root hasn’t pith, in center of root is sclerenchim

Root Anatomy - Dicot Roots

Epidermis

• Dermal tissue
• Protection of the root

Cortex

• Ground tissue
• Storage of photosynthetic products
• Active in the uptake of water and minerals

Endodermis

• cylinder once cell thick that forms a boundary between the cortex and the stele
• contains the casparian strip, and conductive cells

Pericycle

• found just inside of the endodermis
• may become meristematic
• responsible for the formation of lateral roots

Vascular Tissue

• Xylem and Phloem
• Forms an X-shaped pattern in very center of root

In dicot roots, the xylem tissue appears like a 3-pronged or 4-pronged star. The tissue between the prongs of the star is phloem. The central xylem and phloem is surrounded by an endodermis, and the entire central structure is called a stele.

Anatomic structure of stems and rhizomes monocotyledones and dicotyledones.

A stem is one of two main structural axes of a vascular plant. The stem is normally divided into nodes and internodes, the nodes hold buds which grow into one or more leaves, inflorescence (flowers), cones or other stems etc. The internodes act as spaces that distance one node from another. In most plants stems are located above the soil surface but some plants have underground stems.

Stems have four main functions which are:

• Support for and the elevation of leaves, flowers and fruits. The stems keep the leaves in the light and provide a place for the plant to keep its flowers and fruits.
• Transport of fluids between the roots and the shoots in the xylem and phloem.
• Storage of nutrients.
• The production of new living tissue. The normal life span of plant cells is one to three years. Stems have cells called meristems that annually generate new living tissue.

Stem structure

Stem usually consist of three tissues, dermal tissue, ground tissue and vascular tissue. The dermal tissue covers the outer surface of the stem and usually functions to waterproof, protect and control gas exchange. The ground tissue usually consists mainly of parenchyma cells and fills in around the vascular tissue. It sometimes functions in photosynthesis. Vascular tissue provides long distance transport and structural support. Most or all ground tissue may be lost in woody stems.

Monocot stems

Vascular bundles are present throughout the monocot stem, although concentrated towards the outside. This differs from the dicot stem that has a ring of vascular bundles and often none in the center. Monocots rarely produce secondary growth and are therefore seldom woody.

Most monocots are herbaceous plants that do no attain great size. Stems have neither a vascular cambium not a cork cambium, and thus produce no secondary vascular tissues or cork. As in herbaceous dicot, surfaces of stem arc covered by an epidermis, but xylem and phloem tissues produced by procambium appear in cross-section as discrete vascular bundles, scattered throughout stem. Type of vascular bundle is closed collateral.

Rhizome of monocot has three zones: dermal, primary bark and stele in cross section. Dermal tissue is epidermis. Primary bark consists of oval crumbly cells of ground parenchyma, cells of endodermis is horseshoe-like and endodermis is doubled (it is a diagnostic feature of lily of the valley). There are two types of vascular bundles in stele: closed collateral (near pericycle) and concentric centerphloem, which are chaotically arranged in parenchyma. Pith is in the centre.

Monocot stems differ from dicot stems in that they lack secondary growth

• No vascular cambium nor cork cambium
• Stems usually uniform in diameter
• Scattered vascular bundles (not in a ring like dicot stems)

Monocot stems, such as corn, palms and bamboos, do not have a vascular cambium and do not exhibit secondary growth by the production of concentric annual rings.

The following illustrations and photos show scattered vascular bundles in the stem cross sections of corn (Zea mays):

A cross section of the stem of corn (Zea mays) showing parenchyma tissue and scattered vascular bundles. The large cells in the vascular bundles are vessels. [Magnified Approximately 250X.]