Coloring flowers

Overview:
Use colored dyes to follow water up a plant's stem and into the petals (transpiration).

Equipment:
1. White flowers - Queen Anne's Lace or white carnations work best.
2. Water-soluble food coloring, from the local grocery store - blue and red work best.
3. Container.
4. Knife to split the stem if you want to experiment further.

Safety:
Be careful with the knife if you cut the stem.

How to do the experiment:
1. Add food coloring + water to the container in which you'll place the white flowers. Put the flowers in the container.
2. Wait 6-12 hours, and observe. For a better idea of what goes on, check back every few hours to note the level of the food coloring in the plant. Depending on the length of the stem, the white petals should ultimately turn the color of the dye added to the water.
3. If you want to experiment further, split the stem into 2, or into thirds, and place each section in a container with different food coloring (white carnations with blue/red/yellow produces an interesting effect. Observe results.

Explanation:
The leaves and some petals of plants contain many small pores, called stomata or stomates (singular: stoma or stomate). Water evaporates through these pores. As it does so, the plant draws water through its stem, and ultimately from its roots via the surrounding soil (or from the water in the vase). This process of water loss from the plant is called transpiration. Water movement through the plant occurs in xylem, hollow cells stacked end to end to form tubes. In leaves and thin stems, the xylem occurs in vascular bundles that also contain phloem, which transports organic compounds throughout the plant. In leaves, vascular bundles are termed veins. Blue or red dye is very good for outlining the xylem in the plant as it draws the water + dye up the stem. You can see it quite clearly if you cut the stem and look at it in cross-section.

Useful References:
MadSci Botany Links

Further comments:
To experiment further, try repeating the experiment altering different conditions:

1. What is the effect of temperature on the process of transpiration? For example, how fast does the dye travel if the flower is kept in the refrigerator vs. at room temperature. You should try your experiment with 3 plants at room temp and 3 kept in the refrigerator. Measure the distance the dye travels every hour.
2. Do different dyes travel at different rates? How can you explain any difference you see?
3. If you place the flowers in normal water, water + 1% sucrose (table sugar) and in a 5% sucrose solution, does the presence of sugar affect the rate at which the dye travels? Why?