Root and Stem Morphology:
a study of the appearance of the roots and stems of plants.

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The ability of plants to grow and produce depends inescapably on the soil, from which their roots absorb the water needed for photosynthesis, as well as the mineral elements required for growth and cell functions. Roots also anchor the plant in the soil so it can hold itself upright and serve as a storage area for excess food. Roots therefore perform both mechanical and transport functions and contain structural features serving each.

Water absorption by roots is basically an osmotic process. As roots transport mineral nutrients into their xylem, the solute concentration in the xylem increases. This causes osmosis of water from the soil into the xylem through the membranes of intervening cell layers. Transpiration pull, caused by evaporation of water from the leaves, removes water from the root xylem causing water to move into the root from the soil. In terms of water potential, the removal of water from the root by transpiration pull reduces the water potential in the root xylem, creating a water potential difference between the soil water and the root xylem that drives inward water flow. The structure of roots gives them a rather large surface area to compensate for the slowness of uptake by any one root and provide an adequate total uptake of water. This osmotic absorption mechanism enables plants to take up water from soil that appears macroscopically to contain no liquid water and cannot be used as a water source by animals.

Regions of a root:

regions and tissues of a root

Tissues of a root: link to a local picture

primary root growing from the seed

Types of roots:

root systems Types of root systems:

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Stems: support flowers and leaves and provide transportation within the plant.

Most plants produce ordinary leafy stems with appendages such as leaves, and flowers growing from their nodes. These plants are called caulescent. A plant with basal leaves (either a very short stem or no above-ground stem) and a leafless flower stalk is called acaulescent. A young stem or twig of a flowering plant is marked by the presence of nodes, the points on a stem where a leaf or leaves are attached. The intervals between the nodes are called internodes. Although the root and stem share many common structural features, the root bears no appendages comparable to leaves, and consequently, has no nodes or internodes.

Three main stem types:

  1. Herbaceous stems have very little woody tissue. The epidermis is very similar to that of leaves, being a single cell layer that secretes a waxy cuticle onto its outer wall.
    • Monocot stems have numerous vascular bundles scattered throughout the stem The xylem of each vascular bundle is located in the half of the bundle toward the center of the stem, while the phloem occurs in the half toward the outside surface of the stem. Each bundle is surrounded by a sheath of elongated, heavy-walled sclerenchyma fiber cells, which provide mechanical support for the stem.
    • Dicot stems have vascular bundles arranged in the form of a cylinder, around a central core of parenchyma tissue called the pith. The tissue outside the vascular bundles is called the cortex. The outer edge of the cortex, just beneath the epidermis, functions mainly in the mechanical support of the stem.
    • Herbaceous stems live for different lengths of time:
      • Annual plants - live for only one year.
      • Biennial plants - short-lived plants that produce only vegetative growth the first year, then bloom the second year.
      • Perennial plants - live for an indefinite period of years and bloom every year after the first.
  2. Woody stems have a high percentage of woody tissue. link to an Internet WebsiteA continuous vascular cylinder develops in a young woody stem. Leaf traces, strands of vascular tissue, extend from gaps in the vascular cylinder at the stem nodes and travel outward toward leaves and twigs. These gaps are soon closed by secondary growth, resulting in a solid cylinder of xylem and, to the outside of it, phloem. Between the xylem and the phloem lies the vascular cambium, a thin sheet of dividing cells which causes the growth in diameter of the stem. The xylem portion of the stem, as it becomes more massive by further secondary growth, becomes what we recognize as the wood of a tree. The tissues outside the wood and the cambial layer are called the bark. Its inner part comprises the tree's phloem, while the outer bark consists of multiple layers of tough protective tissue called cork.

  3. Shrub has several woody stems growing from a single base.

stem modifications Stem modifications:

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To complete the picture of how roots obtain water and minerals we must consider the structure and properties of soil. Soil is the combined product of the weathering processes by which rocks are degraded and the biological processes by which organic material is formed at the earth's surface.

Soils contain the following materials:

A soil's ability to supply mineral nutrients, chemicals other than carbon, hydrogen, and oxygen, is the principal factor in its fertility. Essential elements are those that are required for the growth of healthy plants. Macronutrients are elements required in relatively large amounts. Micronutrients, or trace elements, are needed only in minute amounts. Despite the small amounts needed, the requirement for most micronutrients is just as absolute as for macronutrients.

Element Concentration
(relative units)
Role within the plant
formation of proteins & nucleic acid
formation of enzymes
proper functioning of cell membraines
formation of nucleic acids and ATP
formation of proteins, coenzymes for carbohydrate metabolism
essential for chlorophyll synthesis
formation of cell wall in meristems
formation of oxygen in photosynthesis
cell respiration and nitrogen metabolism
Formation of enzymes used in respiration and photosynthesis

Due to the frequently marginal supply of, and competition for, nutrient elements in nature, it is important for plants to reuse essential nutrients internally. When a leaf grows old it turns yellow, reflecting the breakdown of chlorophyll as well as most of the leaf protein. Most of the nitrogen from these compounds is recovered by plants before the leaf is shed. The export of nutrients from leaves occurs in the phloem. The recovered nutrients are stored in the stem or roots of the plant for use in the next year's spring growth.

Research Links:










Phloem is the food-conducting tissue in plants.
Food is mainly produced in plant leaves and must be carried downward to the rest of the plant. Remember that something "flows" downhill. Flow - Phloem










Perennial plants have herbaceous stems, live for an indefinite period of years, and bloom every year after the first.










The most important type of water in the soil is capillary water.
This is the water that is most often available for uptake into plants.