Structure of Dicotyledonous Stem

IB Assessment Statement Draw and Label plan diagram to show the distribution of tissue in the stem and leaf of a dicotyledonous plant.

What is a Dicotyledon? Dicotyledons: a type of flowering plant with two embryo leaves (2 cotyledons)

What Exactly is a Stem? Before we go any further in this presentation, let’s define a stem. A stem: is generally considered to be the central axis of the plant. supports the leaves and flowers of a plant. has nodes from which new shoots and sometimes new roots can arise. is usually found above-ground, but can be modified and found below-ground as well.

Function of Stem Stems connect the leaves, roots, and flowers of plants and transport material between them using xylem and phloem. Stems provide support.

How do stems provide support? Cells absorb water and high pressure develops inside the cell. This is cell turgor and it makes cell almost rigid. Some cells develop thickened cellulose walls which strengthens the plant Cell Walls in the xylem tissue are both thickened and lignified making them very strong. Xylem provides support especially in woody stems.

Tissues in the Dicotyledon Stem Epidermis: surface of the stem made of a number of layers often with a waxy cuticle to reduce waterloss. Cortex Tissue: Forming a cylinder of tissue around the outer edge of the stem. Often contains cells with secondary thickening in the cell walls which provides additional support.

Tissues in the Dicotyledon Stem Vascular bundle: contains xylem, phloem and cambium tissue. Xylem: a longitudinal set of tubes that conduct water from the roots upward through the stem to the leaves. CELLS are DEAD! Phloem (sieve elements) transports sap through the plant tissue in a number of possible directions. CELLS are alive!

Tissues in the Dicotyledon Stem Vascular cambium is a type of lateral meristem that forms a vertical cylinder in the stem. The cambium produces the secondary xylem and phloem through cell division in the vertical plane.

Tissues in the Dicotyledon Stem In the centre of the stem can be found the pith tissue composed of thin walled cells called parenchyma. In some plants this section can degenerate to leave a hollow stem.

Real Photo

Monocot stem

Growth and Development of Stems Plants grow is restricted to 'embryonic' regions called meristems. Having specific regions for growth and development (restricted to just the meristematic tissue), contrasts with animals in which growth takes place throughout the whole organism.

IB Assessment Statements State that Dicotyledonous plants have apical and lateral meristems Compare growth due to apical and lateral meristems in dicotyledonous plants.

Two type of Meristem Tissue In dicotyledons there are two types of meristem tissue: Apical Meristem Tissue -- Lateral Meristem

Two type of Meristem Tissue Apical Meristem Tissue -- at the tops of roots and shoots allows them to elongate (get longer)

Two type of Meristem Tissue Lateral Meristem , also called cambium -- located in the cambium in the vascular bundles, makes roots and shoots thicker, with extra xylem and phloem tissue

Stem modifications Bulbs (plant can regrow from it; tulip) Tubers (thickening under the ground storing food; potato) Rhizome (ginger) Stolons (stem runs parallel to the ground, producing roots at its ends)

Tubers A tuber is an underground stem that stores food. We know a potato is a tuber because it has nodes (eyes) which produce new shoots. A potato is a tuber

Bulbs Bulbs come in 2 basic types: Tunicate bulbs; onions and tulips are examples. Scaly bulbs; tiger and asiatic lilies are examples.

Tunicate Bulbs Tunicate bulbs have: A papery outer covering called a tunic. A compressed, modified stem with nodes, called a basal plate. Fleshy scales made of modified leaf tissue. A tunicate bulb

Rhizomes Rhizomes are: underground stems. horizontally-growing. produce shoots and adventitious roots. Iris rhizome

Rhizomes Some plants, like quack grass, produce long, thin rhizomes.

The pachymorph rhizome of Ginger Rhizomes Other plants, like ginger, produce large, thick rhizomes called pachymorphs. The pachymorph rhizome of Ginger

Stolons Stolons are: Aboveground stems. Grow horizontally. Produce shoots and adventitious roots. Strawberry and Spider Plant are examples of plants that produce stolons.

Stolons Wild Strawberry stolons

Your turn… You will observe and make detailed drawings of: Monocotyledonous stem – corn Geranium – older dicot Tilia, two year old stem (lateral growth) Tilia, three year old stem (lateral growth) Acorus Rhizome

Animation on Secondary Growth http://bcs.whfreeman.com/thelifewire/content/chp35/35020.html