Monday 25 March 2013

When science goes "wrong"

Some time ago, we tried putting white flowers in coloured water so see if the colour of the petals would change as water flowed up the xylem.
We failed but I had used carnations which were well past their best so perhaps that was why.

Recently, I saw this activity again and decided to have another go.

This time, I purchased a fresh pot of white chrysanthemums.

We cut off three long stems and immediately put them into

  • water
  • green food colouring with water
  • purple food colouring with water
Due to our enthusiastic use of food coloring for our ice activities these weren't full bottles and so had some water added to them.

After an hour and a half, nothing had happened so I started another stem using a whole bottle (38ml) of red food colouring.

Results after five hours:

Not any different. So what went wrong?

I suspect this is partly due to the ambient temperature. Our heating is set to 18 degrees Celsius but it is likely that the kitchen window where these are sitting is not as warm as this as we are having a very cold snap, here in England, at present. Transpiration will be slower at this temperature leading to a slower flow of colour through the xylem. If this is the case, my flowers should turn colour slowly.

An alternative explanation would be to do with the food colouring used. I used the Silver Spoon colours. It is possible that other manufactures produce more concentrated food colouring.

I'm fascinated about any other explanations. This is a well tried activity so why can't I get it to work?
The science hasn't really gone "wrong" just there must be another factor probably temperature.

Added a week later:

These are the rather sad flowers after a couple of days. Note how wilted the plant in the red, second from left, is. This is the flower in pure colouring. Once I read the bottle, it turns out that theses colour have as their main ingredient glyerol. This must be the reason why the experiment failed. Glycerol has a high osmotic pressure and will dehydrate the cells. It also explains why colour didn't seem to get to the petals. Moral is to try again with colouring with a different base.


  1. I tried that experiment a couple of years ago. It took a day or two to show faint results. However, last month I took a couple of stalks of celery (with leaves) and did the experiment with about a tsp. of blue food colouring (what I had on hand)in a jar of water. By the next day, results were beginning to be seen. I left it in the coloured water for over a week to enjoy it. The nice thing about celery is that if you look at the bottom of the stalk, the tubes can be seen that carry the water up the stem.
    Myra from Canada

    1. Thank you-I need to try this with celery. I like the idea of the colour being seen as it travels.