The Plant

They not only help to provide the air we breath, but clean it as well!

Plants have been divided into two Categories based on how they reproduce. These groups are called - Gymnosperms and Angiosperms.

Gymnosperm, or Naked Seed: The Category of seed-bearing plants without flowers. There are several types, but the most common are the coniferous plants. The seeds are not enclosed in a fruit, but are borne upon seed scales arranged in Cones. The seeds develop within the Cones and shortly after the seeds mature, the protective scales of the Cone open up and the seeds are released. Distributed world-wide with the majority in Temperate and Sub-Arctic regions, this Category are the most ancient of our seed bearing plants.

Angiosperm, or Enclosed Seed: These are the flowering plants. Appearing after the Gymnosperms, it is believed that the Magnolia was the first of this Category that now includes countless shrubs, herbaceous plants, grasses, broadleaf trees and specialized plants such as succulents, and aquatics. With well over a quarter of a million known species, Angiosperms have colonized and adapted to every region in the world. They have become so successful they are now the most dominant form of plant life and form a major food source. Following fertilization of the Ovule, the seeds develop within the protection of the Ovary. The Ovary enlarges into a fruit as the fertilized seeds grow. Perhaps the secret to their success is that Angiosperms have two sub-classes that have formed as a result of environmental adaptations:

Dicotyledons; have floral organs in multiples of four or five. The leaves have a netlike vein pattern, and the vascular tissue inside the stem is arranged in a ring. This group of plants consists of trees, shrubs and most herbaceous plants. Seedlings have two seed leaves or Cotyledons, for nourishment until its true leaves develop. The stem and root expand with secondary growth.
Monocotyledons; with the floral organs generally occurring in multiples of three. The veins in the leaf are parallel, the vascular system inside the stem is scattered, and as such the plants produce no secondary growth. Consist of grasses, bulbs and palms. Germinated seedlings have one Cotyledon.

Vascular Plants (Tracheophytes), are made up of Rigid Walled Cells. These Cells exist in many shapes, variations and sizes, and when organized into functional units form Tissue. Each type has a particular function to perform.

At the center of a Cell is the Vacuole, filled with Cell Sap - containing nutrients, metabolites, and waste products. Surrounding the Vacuole is the living 'soup' of the Cell, Cytoplasm, within which are varying Organelle, proteins, carbohydrates and salts, including; Mitochondria - converts energy into forms that are usable by the cell, Nucleus - contains the DNA responsible for providing the Cell with its unique characteristics and Chloroplast - (see below). A semi-permeable membrane allows water and salts in, whilst keeping the Sap and Cytoplasm within.

New Cells and Tissue are formed at growing points called Meristems. This tissue of actively dividing cells is located at the tips of the stem or roots, where they are responsible for the primary growth of plants, or in the Cambium layer, (see below) where they are responsible for secondary plant growth or 'thickening'.

The Vascular System:
At the center of the Dicotyledonous stem is the Pith, which is surrounded by Cambium Tissue. It is in this layer that new Cells are formed. During the growing season the Cells in the Cambium Layer divide actively, producing new Cells that differentiate into Xylem, toward the inner side of the Cambium, and Phloem toward the outer side. Arranged in columns called Vascular Bundles, this is the Conducting Tissue that is responsible for transporting water and nutrients to all the Cells of the plant. The Vascular Tissue is surrounded by the Cortex or Ground Tissue, which is all protected by a layer called the Epidermis. Growth of trees & shrubs depend on successive layers of Woody Tissue to the stem of the original young seedling due to the increase in Xylem Cells. A new Cambium Layer, called the Cork Cambium develops outside the Phloem and produces successive layers of Cork Cells that protect the stem.

The Tissues of a Monocotyledonous plant stem are similar, the big difference is the arrangement of the Cortex and Vascular System. The Cortex and Pith is replaced by Parenchyma Cells. The Parenchyma has air spaces within it's Cells allowing for an exchange of gases to take place. Surrounded by a layer of Sclerenchyma Cells, the stem is encased within the Epidermis. As the Sclerenchyma Cells die off on reaching maturity, the thick, heavily lignified wall that encased them remains to strengthen and support the stem. There is a layer of tough Sclerenchyma around the Vascular Bundles that are scattered throughout the Parenchyma. The Vascular Bundles do not contain Cambium Tissue resulting in no secondary thickening or Wood to form.

• Xylem Tissue:
Conducts soil solution up the plant from the roots.
Builds up in woody perennials to form the wood.
• Phloem Tissue:
Conducts manufactured food from the leaves.
Transports this food throughout the plant.

The Dermal System:

Dermal Tissue forms the Epidermis or skin of the plant. The Lower Epidermis of the Leaf contains Stomata. These are openings through which water is lost and the gases Carbon Dioxide and Oxygen are exchanged with the atmosphere; given the term Transpiration. These openings are surrounded by specialized Cells called Guard Cells. The Guard Cells expand in extreme weather conditions or contract in desirable conditions. This will alter the size of the openings and thus regulate Transpiration. The Epidermis is covered with a waxy coating called the Cuticle, a waterproof layer reducing water loss from the plant surface through Evaporation.