Beginning at the Bottom
Water is absorbed through the roots of a flower. These roots are called "hair roots" because they are fine and thin. You can find hair roots on bulbs, tubers, rhizomes and traditional branching roots. The water molecules pass through the epidermis, or skin, of the hair roots and move into the main root--sometimes called the tap root--of the flower. There, they mix with nutrients from the soil and move up the stem of the plant. In the case of cut flowers, which do not have roots, the water enters the stem immediately. If you color water before placing a white flower into the water, you will be able to see the path of the water as it travels through the flower.
Water is not sucked up the stem of a flower like a person would suck a liquid through a straw. Instead, water molecules move up a flower stem because they are also evaporating through the surface of the flower's leaves. As water molecules evaporate, more crowd in to take their place. In addition, water molecules naturally "stick" to each other. In flowers, however, they are more attracted to the tubes, or capillaries, than to each other, so they move through the tubes rather than clumping together. This is called "capillary action."
As the water molecules move up the stem, they also branch off to travel through the flower's leaves and to the bud of the flower. When they reach the leaves, the water molecules and nutrients will aid in the process of photosynthesis, or food-making. A large percentage of the water will also evaporate to make room for new water to move in. Without water, the plant cells will not swell and the flower will not bloom. In fact, the motion of the water molecules moving through the flower keep it upright. Flowers that are thirsty wilt and droop. Flowers cannot live on water alone, however, or cut flowers would last a long time. Flowers also need nutrients to grow and perform photosynthesis; nutrients that can only be found in soil. Without these nutrients, they will die in a matter of days or weeks.