|MadSci Network: Botany|
You are correct that a sugar solution is thicker than water but I don't think that is why you failed to get the dye to move up the stem and into the flower. Plant cells attract water by having higher concentrations of salts or other dissolved substances in their cells than in the soil solution. Water moves from a high concentration of water (less salty) to a lower concentration of water (more salty) across a cell membrane. Movement of water across a cell membrane is termed osmosis. The osmosis website cited under References gives a good definition except for the term "semipermeable", which is inaccurate and obsolete. The membrane is selectively permeable, meaning water can freely cross the membrane but most salts and sugars cannot freely cross. Salts and sugars would have to be actively transported across. Sugar works like salt so I think your sugar solution was more concentrated than the solution in the flower cells so water (carrying dye) could not move into the flower cells. It may be that some of the water in the cut flower moved out of the cut flower and into the sugar solution. Did you notice any wilting of the cut flower in the sugar solution? Cut flowers absorb dye solutions faster if they are slightly wilted prior to placing their cut ends in a dye solution. Smaller amounts of sugar are added to vase solutions for cut flowers after dying. The sugar provides energy to the flower and helps them last longer. References Osmosis Re: What will happen to flowers if you put them in salt water? Re: Do different dyes travel at different rates? Re: why is yellow food colouring sucked up by flowers more quickly? Re: Can flowers be dyed with food coloring while still Re: If I water plants with colored water will it change the color of the plant? Re: Why does a carnation turn two seperate colors?
Try the links in the MadSci Library for more information on Botany.