|MadSci Network: Botany|
You certainly have an interesting observation. I assume that the 150 degree F temperature has no effect on the dye itself. You could confirm that by allowing the dye solution to cool and then see of it colors the flowers as well as the 80 degree F dye solution that was never heated. One possibility is that cells at the base of the stem are being damaged by the heat and water is not moving up the stem to the flower. It seems likely the hot water would cool before it gets to the flowers. Do the flowers in hot water wilt after the treatment? If so, that would indicate the stem base was being damaged by heat. If you later place previously heat-treated flowers in room temperature dye, does the dye then color the flowers? If not, then that would also confirm heat damage to the stem. Another effect that may be involved is that air solubility in water decreases as the temperature increases. This could possibly result in air bubbles forming in the flower stem xylem and cause an air blockage to water flow. This is termed an air embolism. Cut flower stems are recut under water in order to remove any air embolisms. Another possibility is that the hot dye is being bound or inactivated as it passes through the flower stalk, possibly by heat-damaged cells or substances that leak out of them. Do you get the same results with all dye colors? Have you tried splitting the base of a flower stem and placing half the split stem in one temperature dye and the other half in the other temperature dye? Technically, you are not dealing with capillary action. Capillary action is not really responsible for upward movement of water in intact plants or food coloring in cut stems of living plants. Capillary action occurs in initially empty, small diameter tubes with both ends open. The empty tube is stood upright with the bottom end just under the surface of water, and water moves up the empty tube. The smaller the tube diameter, the higher the water rises. Unless you cut both the top and bottom of the stem and the plant xylem is empty of water to begin with, in which case the plant would most likely be dead, then it does not meet the conditions for capillary action. What occurs in water and dye uptake by cut flowers is mainly water flow in response to a water potential gradient from vase to stem to flower. Dye is mainly carried along with the water, although there may also be some diffusion of dye. Water moves from higher to lower (more negative) water potential. It is recommended to slightly wilt the cut flowers prior to dye application in order to speed water uptake by the flower. Reference Postharvest of Cut Flowers
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