White roses are my favourite flower, because you can turn their petals into rainbows with some simple science.
It’s common in high schools to teach transpiration using a stick of celery in water coloured with blue food dye. This is because the xylems in celery are very big, large enough to see with the naked eye.
The xylem is a vessel. Much like how our blood vessels carry blood from our heart to our lungs, around our body, and back, plants have vessels too.
The xylem is a plant’s water vessel. It allows water to move from the root to the leaves, a process called transpiration.
You can see this in action using celery over a day or two, but if you have the patience you can get some very impressive results using a white rose.
The way the water moves is very simple, but very clever. The movement of water out of the leaf to evaporate in the air, causes the water behind it to move up to take its place.
Much like a conga line, the water molecules adhere to each other and the sides of the xylem. They can only go forwards to where more room is made for them – the exit. This action allows water to be pulled up from the roots to replace the water lost from the leaves.
The xylem runs through the entire stem and all the leaves, which is why cut flowers can last a few days before they wilt – they can continue to pull water up through the xylem for a short time before the plant begins to die.
If you take a long stemmed white rose, carefully split the bottom few centimeters of the stem into two or three and place each end into a different colour water, the coloured water will be pulled up through the xylem as water escapes the leaves through transpiration.
This water has to be provided to the petals too, so eventually the petals will take on the colour of the water they are being provided with.
There is more than one xylem in every plant, in flowering plants like roses they are so small you can’t see them without a microscope. The petals are supplied with water by different xylems, so you should see a very colourful pattern emerge as the coloured water reaches them.
Take the time to teach your kids a little about transpiration this school holiday, and decorate your home with multi-coloured roses too!
About Elinor Wyn
A communicator by profession and vocation. I worked as a high school science teacher in the UK for four years before moving to Australia to try something new. Communicating new ideas is not a vocation I could ignore, and I completed my Masters of Journalism at QUT in 2015. Since then I have written science articles for my blog, and I have worked for a not-for-profit organisation, writing articles for their website. I learned a great deal about the barriers to employment faced by people with disability. I worked hard to source and create articles for that organisation, which would help to break down those barriers. Science communication has always been at the core of what I do. My experience as a teacher taught me how to summarise complex research into more accessible, jargon-free language. Now I continue to do some casual work in the not-for-profit sector, but I also work as a freelance journalist.
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