Did you ever do this experiment in elementary school? I tried to find carnations, but I didn't have any luck. I ended up with white daisies, and I let the boys choose the colors for the dye: we went with orange and teal. We mixed a few drops of food coloring and water in separate jars.
We read about how plants suck up water through thin tubes inside their stems. Using some of our
Sonlight science books (
Biology Level I by R. W. Keller,
The Usborne Library of Science World of Plants, and
Usborne Starting Point Science, volume 1), we learned that plants have a system of vascular tissue in their stems which carry water and minerals up and down the stem.
Xylem and
phloem surround the central core, the
pith, in many plants. Food and water is stored in the pith. The xylem carries water and minerals upward from the roots, and the phloem brings food from the leaves (via photosynthesis) down to the lower parts of the plant. To see this in action, we placed the white daisies in the jars of colored water and waited.
After several hours, we could already see tiny lines of color in the petals, like veins.
It took a couple of days for more noticeable results. The color is very faint, but we can see a change. I remember carnations having a more dramatic result when I did this experiment as a kid. If I can find some, we might do this experiment again.