Introduction to the Plant Body

The Plant Kingdom includes a vast number of different kinds of plants, and a number of Plant Divisions or Phyla (The classification category below Kingdom). Before we begin our discussion of tissues and the unit on plant structure and function, it will help to give a little background about plant classification and the organization of the plant body. We will return to the subject of classification during our diversity unit in more depth.

The Plant kingdom is organized by increasing complexity, using two main features:

  • Dispersal Means
  • Conducting, or vascular tissue

    The most "primitive" or less complex plants disperse, or spread to new areas with a single cell structure called a spore . The more complex plants (conifers and flowering plants) disperse with a multicellular seed , which contains a supply of nutrients as well as an embryo, protected by a seed coat, and with flowering plants, a fruit.

    The simpler plants, which include mosses and liverworts, do not have special conducting or vascular tissues, so all water and nutrients must pass from cell to cell throughout the plant. This limits the size of mosses, especially vertically. In addition, as we will see, a second function of vascular tissues is support. Mosses, lacking this support would have a difficult time being tall.

    Plant Organization
     The typical plant is organized along an axis - with continuous growth originating from both ends (or tips) of the axis. This growth, as mentioned takes place in special cell division regions called meristems.

    Plants, in general, exhibit open growth , or continuous growth from their meristems of embryonic origin until they die. At all times the tips of plants are essentially embryonic, with active meristems, while other regions may be up to 1000's of years old.

    For our unit on plant structure and function, we will focus on the "higher" plants, and especially the flowering plants. The most distinctive features of flowering plants are their reproductive features. The reproductive organ is the flower . Following reproduction, the embryo and seed are enclosed within a fruit (which develops from the ovary tissue of the flower. We will talk about how all this happens in the next unit.

     In addition, flowering plants are divided into two broad groups, which differ from each other in many anatomical ways, the Monocotyledons (Monocots) and the Dicotyledons (Dicots). These are important to learning about plant structures. It will make your understanding of plant structure a little easier if you have this introduction first.

     The Two Groups of Flowering Plants:
    Monocotyledons Docotyledons
    Flower parts in 3's Flower parts in 5's (4's)
    Leaves with parallel veins Leaf venation palmate or pinnate
    No true cambium Cambium usually present
    One cotyledon (seed leaf) Two cotyledons (seed leaves)
    Scattered vascular bundles Vascular bundles in a ring (cylinder)
    Sheathing leaf bases Leaves usually have a petiole
    All of this should make more sense when we look at roots, stems and leaves during the next week or so.



    Plant Life span and Sturdiness of Plants
    The so-called higher plants (or seed plants) are either herbaceous or woody. Woody plants (shrubs and trees) have significant woody (or tough) parts above the ground which persist year after year. Herbaceous plants do not have such strong, woody parts which persist year after year, and are rarely as large as the woody plants. Plants can complete their life cycle in from one to several growing seasons.

    There are two major systems in the typical plant
    Root System

    Shoot System
     Roots, stems and leaves are the organs of plants, just as we have organs in animals. We will spend considerable time looking at these structures in the next few weeks, once we learn the cells and tissues from which they are constructed. Leaves, stems and roots are organized into regions, and plant tissues are located in precise ways within these regions. This actually makes learning about plant structures pretty straightforward.

    Root (From outside to interior)


    Stem (From outside to interior)
     Dicot
     Monocot

    Leaves (Top to Bottom of Leaf)
     Dicot

    Monocot

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