How do flowers make nectar?

Plants use the energy in sunlight to make sugar from carbon dioxide and water -- the process that's called photosynthesis. Most of the sugar is made in the leaves, the plant organ that is specialized to gather sunlight. From the leaves this sugar travels through the plant's conducting tissues to the other parts of the plant -- the roots, stems and flowers. These plant parts then remove the sugar from the conductive tissues and use it to fuel all their metabolic processes. In the flowers there are specialized cells, usually found at the base of the flower, around the ovary. These cells secrete the sugar into a sweet droplet of fluid that we call nectar. That's what you taste when you pick a honeysuckle blossom and suck on it. And that sugary solutions is what the hummingbird as well as many insects are after. The flower produces nectar at a rate that varies with the temperature and time of day, and the nectar will accumulate if no bird or insect visits visits the flower. So the amount of nectar present in the flower depends on how rapidly it is produced and how often it is removed by hummingbirds or bees. When most of the nectar is removed it takes a while for the supply to be replenished.