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(awk′sĭn) [Gr. auxe, increase]
A substance that promotes growth in plant cells and tissues.


a type of plant growth-regulating substance involved in the growth of cells and several other functions. The most important auxin is indolacetic acid (IAA; see Fig. 194 ), but many other substances have been classified as auxins, using a BIO-ASSAY method developed by Fritz WENT.

The effects of auxins depend on their concentration in the plant. They are most concentrated at the shoot tip and least concentrated in the root, except for small amounts at the root tip. The major effects of auxin are summarized below:

  1. Encourages cell growth by elongation, producing a softening of the MIDDLE LAMELLAE of cell walls.
  2. Stimulates cell division in the PHLOEM of the VASCULAR BUNDLES, so encouraging new growth.
  3. Promotes positive PHOTOTROPISM in shoots by growth of tissues towards the light source.
  4. Promotes GEOTROPISM in all parts of the plant (positive in roots, negative in shoots, due to unequal distributions of the hormone).
  5. Induces APICAL DOMINANCE by suppressing lateral buds.
  6. Induces lateral root formation.
  7. Stimulates fruit development, enabling seedless fruits to be produced artificially. (h) Suppresses ABSCISSION in leaves and fruit. (i) Encourages the formation of wound tissues in injured or diseased plants.

    Auxins have a number of commercial uses, e.g. to promote the rooting of cuttings, regulate plant height, induce flower formation and control fruit set and fruit drop.

References in periodicals archive ?
Photo: 1 Moisten two large handfuls of sphagnum moss (less for a smaller plant); sprinkle with rooting powder
Remove the little half-moon-like leaves surround the joint and dip the bottom of the cutting in hormone rooting powder. Arrange several cuttings around the rim of a 5in pot filled with gritty compost and root them in a heated propagator or under a polythene tent on a warm shady windowsill.
Snip non-flowering, 8-10cm shoots just below a node and dip them in rooting powder. Plant into seed and cutting compost until rooted, keeping them in a mini cloche, or place a plastic bag over the pot to keep in the humidity.
If you're taking cuttings from evergreens such as escallonia, remove the lower leaves and dip the base of the cutting into a hormone rooting powder.
Remember to use a sharp knife when preparing the cuttings, treat yourself to some new rooting powder, use clean containers and fresh compost and keep the young cuttings away from direct sunlight until they are well rooted.
The base of the cutting is then dipped in hormone rooting powder.
Trim them just below a leaf joint, making them about 4cm long and dip the cut in hormone rooting powder before inserting them into individual pots of compost.
Choose newer shoots, remove the bottom leaves and cut the rest in half to reduce transpiration, then dip in rooting powder.
Don't forget to buy some rooting powder whilst you are at the garden centre.
After the ends have been dipped in hormone rooting powder and surplus powder shaken off, the cuttings are inserted around the edge of small pots.
Officers also discovered rooting powder, 20 bottles of fertilizer, spare light bulbs and a bag of cannabis.
Dip the shoots into enough hormone rooting powder to cover the wounds where leaves have been removed.