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PLANT GROWTH & BIOLOGICAL PHYSIOLOGY.

There are three classes of plant. Each of these classes metabolize in a different way. The first class are succulents called CAM. CAMs like low light and high humidity levels and so thrive indoors, in bathrooms and kitchen areas.

The second class of plant is called C4. They grow in hot arid regions and are very efficient at using both Carbon Dioxide (CO2) and Sunlight. Most C4 organisms are grasses.

The third and last class is called C3. The C3s join two 3-Carbon atoms together to produce sugar. The chemical formula for sugar is C6H12O6 which is 6 Carbon, 12 Hydrogen and 6 Oxygen atoms stuck together. Most of the gardener’s favourites are to be found in this class.

HOW DO THEY WORK?

Like all living things, it breathes 24 hours a day. In order to make energy each one of its cells respires (converts sugars to energy). It uses Oxygen (O2) and expires, or breathes out, Carbon Dioxide (CO2).

In the same way that energy moves around the human body, so water, nutrients and sugars are continually being transported around the plant body. The leaves create a circular flow with the roots. This circulation occurs when the leaves draw up water from the roots, through their Xylem.

These are straw like cells found in the stem. The water continually evaporating from the leaves sucks up more water from the roots and creates the internal water pressure that keeps the plant rigid. Thus if it is deprived of water, as in a drought, it loses its rigidity and begins to wilt when the internal pressure drops.

The leaves return energy to the roots in the form of sugar solutions. These are transported from the leaves via the Phloem. Similar to the xylem, these are also straw like cells found in the plant stem. In this way the leaves exchange sugars for water and nutrients, while the roots exchange water and nutrients for sugar solutions. This liquid circulation is constant and continuous throughout the life of the plant.

THE MAIN PLANT PARTS.

The 3 main parts of a plant are the Roots, the Stems and the Leaves. Each of these parts is of great importance and any problem that arises in any of them will be a major one. The most sensitive part is the roots, as well as being the most difficult to see should a problem occur.

The Roots:

The miracle of growth starts at the roots. As already mentioned, roots transport nutrients up to their leaves and sugars are returned by the leaves. The roots also act as storerooms for the excess sugars that are produced by the leaves. These sugars are stored in the form of starch. The size of the root ball and therefore the amount of starch that can be stored, determines the success of the organism in terms of growth and productivity.

The size of the root system is directly affected by the amount of moisture, the temperature, the available Oxygen and the supply of sugars being transported down from the leaves. According to Graham Reinders, in his book “How to Supercharge Your Garden”, a research Rye plant in a 12 inch pot was said to have had 14 billion root hairs. These hairs would have stretched 6200 miles (nearly 10,000 km) if placed end to end and covered an area of 180ft by 180ft (about 55m by 55m). The greater the root system is the more energy (starch) it will be able to store and so, the more nutrients it will be able to send up to nourish the leaves. It will then have the capability to grow stronger. The end result of this is that the leaves will be able to pass more sugars back down to the roots and so the cycle continues.

Another factor to be taken into account is the root medium. Plants take their nourishment from the medium surrounding their roots. It stands to reason that the less energy it has to expend in order to get that nourishment the more energy it will have available to use for growth and nutrient exchange with its leaves. Because a plant takes most of its water in via its roots, (the root hairs trapping the water molecules surrounding it) and transpires about 99% of that water out via its leaves, it will wilt and fall over if its roots cannot extract enough water out of its surrounding medium.

A plant growing in the ground will take its moisture from the surrounding soil. This moisture normally gets into the soil as rain and the organism absorbs that rain and the nutrients that have dissolved in it, via its root hairs. After the rain has stopped the topsoil quickly dries out as the water filters into the ground. Because of this drying out the plant has developed a means of absorbing Oxygen via its upper roots. The top third of the roots become specialized as “Air Roots” while the bottom third becomes specialized as “Water Roots”.

It is vital to ensure that the Air Roots are not kept constantly wet as this will result in the plant drowning. The Water Roots however, may be kept wet all the time, providing that the water has sufficient Oxygen dissolved in it. Insufficient Oxygen will result in roots with brown, discoloured root tips and subsequent infections. Healthy roots are a crisp, white looking structure.

The plant is quite capable of healthy living with the roots exposed to light as long as they remain moist. However, light will encourage the growth of Algae which will cause odours. The Algae will also compete with the plant for Oxygen during the dark periods and nutrients in the light ones. This, of course will mean that it has to work harder in order to produce sufficient sugars for its needs. The Oxygen produced during the dark periods is used to help the roots convert these sugars, from the leaves, into energy (Starch).

Temperature plays a large part in root growth and function. A lot of the work of the roots is done at night when, because of the lack of light, the green parts of the plant are not producing sugars and distributing the excess to the roots. Roots in a warm environment will function more efficiently than those in a cold one, so those growing in a warm dark environment will inevitably develop better structures than those growing in a cooler one. It has also been found that a constant 24 hour root temperature results in better plant growth than a fluctuating one.

Because plants absorb most of their water and nutrients through the root hairs growing at the tips of the roots and this small area, behind the growing root cap, is constantly advancing, if the plant is allowed to become potbound the damage to the tips will seriously affect the root function. The plant yield is always proportional to the size of the root ball.

The Stems:

The function of the stems is to act as a pipeline between the roots and the leaves. A short stem is a lot more efficient than a long one because the plant needs to use less energy for transportation of sugars. Lifting the water and nutrients up the stem uses a lot of energy. The higher the lift the greater the energy used, so it makes sense to save it by reducing the length of the stem This saved energy can then be utilised by the organism to increase its yield.

The Leaves:

The leaves act as the production area of the Plant. Using water, nutrients and light the leaves combine these ingredients with Carbon Dioxide from the air to produce sugars. Provided that the leaves have sufficient Carbon Dioxide and light the whole organism should thrive.

The leaves are equipped with breathing holes or Stomata, on their underside. These stomata allow the Carbon Dioxide to be taken in. There can be anything from 20,000 to 40,000 stomata on a thumbnail sized section of leaf. These breathing holes are located on the underside for obvious reasons. Firstly, in this position no dirt settling on the leaf can block the stomata. Being on the underside also means that the stomata remain shaded and finally, because they are underneath, they are protected from the ingress of fungal spores.

The leaves only produce sugars and starches when there is light present. Good leaf growth allows more water to evaporate from the leaves and so more nutrients to be sucked up the stems for the leaves to convert to sugars. These sugars are used to provide energy for the plant. The greater the leaf growth the greater the amount of sugar produced and so the greater the amount of energy stored by the roots. The yield of the plant cannot be accurately assessed by looking at leaf growth, because it is the root growth that determines the amount of energy stored.

The leaves are the visible part of the organism and can be a useful indicator of health. The leaves also tell the organism’s life story because they do not repair themselves. An example of this can be seen when a plant is unable to draw sufficient water from its surrounding media. The leaves will lose their turgidity and begin to wilt and then gradually turn yellow as the plant starts to die. If the plant still cannot get nourishment it will eventually turn brown and die





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