Auxins are primarily concentrated in the root and shoot endings. Produced mainly in the buds and leaves of the plant, they promote the elongation of plant cells. The greatest concentrations are found in the root and shoot tips because the greater the concentration of Auxins, the better the growth of the root and shoot will be.
New roots need tis hormone to get started and the shoots tips need them to sustain continued growth. In cuttings this hormone must be redeployed from the shoots to the root beginnings so that the roots can start to grow. Artificial rooting and shooting powders and gels are often used to boost the hormone levels during this process.
It is essential to always use the weakest possible rooting powder or gel. The reason for this is that too great a concentration of Auxins will actually stop the roots from developing. The rooting compound must all be gone within a few days, so this is a definite case of less being more.
One strange thing, which is, as yet, unexplained is the gravitation of the Auxins to the underside of a horizontal branch or stem. This causes the cells on the underside to elongate faster than those on the upper surface, resulting in the stem or branch curving upwards until the vertical is almost achieved and the greatest light is accessed.
On occasions a cutting taken from a horizontal branch will not grow upwards even as it gets older. It is thought that in this instance the cutting of the donor stem has disrupted the message sent by the growth hormone.
Another unexplained anomaly is the action of the hormone on the shaded side of the plant’s shoots. This accumulation of hormone causes the shady side to elongate more than the lighted side and so making the shoot curve towards the light.
The Auxins also accumulate in the top section of the growing shoots, causing the plant to grow upwards towards the light. The main shoots will grow at a quicker rate than their companions. This is because they have the ability to slow the growth of the other shoots by altering the Auxin concentrations. As the dominant shoot grows away from its less dominant companions so its ability to affect them decreases and they can then start to catch up. Should the dominant main shoot be broken or pinched out the Auxins within will be redistributed amongst the other shoots. These shoots will then start to grow stronger.
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