A bulb is that part of a plant that contains the tender shoots of a new plant. Many flowering plants such as tulips, hyacinths, and lilies are propagated by bulbs. The energy a new plant needs to develop is stored in the bulbs. There is a large variation in the size of houseplant bulbs. They can be as small as a pea or as large as 15 pounds (7 kg).  Plants that develop from bulbs produce leaves and flowers each season, then gradually die back and go dormant for a few months. During this dormancy or resting period, the plant stores the nutrients that will help it bloom again the following year. Bulbs can be forced to bloom almost any time indoors, brightening up your house during the cold winter months.