| MadSci Network: Botany |
This is an interesting question. Plants should not be able to take up food coloring added to the soil. The classic experiment with celery petioles and cut carnation flowers has xylem vessels with open ends at the base. This allows food coloring to be easily taken up passively with the water. Intact roots have a Casparian strip that prevents passive uptake of water. All water, mineral nutrients and any other chemicals must first pass through a cell membrane before they can enter the xylem. The cell membranes are selectively permeable. Water passes readily, but other substances do not. What you could do is bareroot the plant and place the roots in food coloring. The roots will probably be damaged enough by the barerooting process to allow food coloring to enter. I once placed some bare rooted chrysanthemum cuttings in a nutrient solution with a red iron chelate (EDDHA) and noticed the new leaves developed a reddish tint. Although the plants stayed in the same solution, the red tint in the new leaves disappeared. The roots eventually sealed off the damaged areas. You could try growing plants in hydroponics and cutting the tips off some roots to allow the food coloring to enter. A good plant to try might be albino corn seedlings. They lack chlorophyll so any food coloring in the xylem should be visible. Another good plant would be jewelweed (Impatiens capensis) which has transparent stems sometimes used in teaching for transpiration experiments. References Casparian strip Albino corn information Impatiens capensis photos Impatiens capensis in Transpiration Experiments
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