Water is transmitted in the stem via very fine tubes and is always under tension. These bubbles lodge near the cut and will restrict water flow to the flower when it is placed in a vase of water. However, sugar enhances growth of fungi and bacteria, but these organisms could be controlled by inclusion of a couple drops of bleach into the solution. Fungi and bacteria, as well as substances they produce, can rapidly clog the fine tubes of the water conduction system. Regular recutting of stem ends prevents the suberization effect.
Flowers are alive even when excised from the mother plant.
Like animals, they need to breathe or respire. Reducing the flowers' temperature dramatically reduces respiration, growth and aging. Stored starch and sugar from leaves and petals provide the energy for flower opening. This is why good growing conditions, proper nutrition, and high light to build food reserves are so important to post harvest flower quality. Sugar is routinely used to open bud-cut flowers before distribution and is included in most flower preservatives.