Floral Tropisms
East Durham College’s informative and colourful exhibit at this year’s Chelsea Flower Show was based on the science of tropism. Led by tutor Allan Raby the students created a display which gave a visual, floral interpretation of one of nature’s most fascinating phenomena.
What is a tropism?
It’s defined as the directional movement of a plant in response to a stimulus. This reaction can be both negative and positive. If the stimulus requires the plant to move towards it, that is positive tropism, if it moves away, then the opposite applies.
How many tropisms are there?
Scientists have identified at least nine types. The East Durham exhibit focussed on five, as follows:
Phototropism
One of the most commonly known tropism, this is when a plant moves towards a light source, either real or artificial. Why? To maximise its potential for photosynthesis. This is very noticeable in Tulips, which are renowned for ‘doing their own thing’ once cut and arranged in water.
Geotropism
Have you ever wondered why seeds, scattered across a surface, always root themselves the right way up, regardless of how they land? That is the effect of geotropism, a seed will automatically right itself, sending roots downwards in search of nutrients, while stems grow upwards towards the light.
Hydrotropism
This is the ability of the roots of a plant to direct their growth towards water, essential for their survival especially during dry spells when the roots will actively move around in the soil to hunt out a water source.
Heliotropism
One of the most fascinating tropism, when a plant will not only rotate itself towards the sun but will actively move position to follow the sun’s trajectory during the course of the day. As in phototropism, this maximizes their chances of photosynthesis. Helianthus (sunflowers) are famous for this very trait.
Thigmotropism
This is when the direction of a plant is a result of a response to physical contact. Ever wondered how a climbing ivy or Clematis find their way around buildings and frames? By using thigmotropism. When the plant’s tendrils find a surface to cling to, that is positive tropism, when they navigate away from an obstacle, that is an example of negative tropism. Roots in soil react the same way if they hit a rock or any other impenetrable object.
Isn’t nature incredible?
Su Whale is a florist and freelance writer with over Thirty years' experience in the floristry industry. She is the author and publisher of three best-selling books: Cut Flowers, 4th edition (2020) Cut Foliage, 2nd Edition, (2021) and Houseplants (2019), all bookshelf essentials for the professional florist.
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