The rice plant usually takes 3–6 months from germination to maturity, depending on the variety and the environment under which it is grown. During this period, rice completes basically two distinct sequential growth stages: vegetative and reproductive. The reproductive stage is subdivided into preheading and postheading periods. The latter is better known as the ripening period. Yield capacity, or the potential size of crop yield, is primarily determined during preheading. Ultimate yield, which is based on the amount of starch that fills spikelets, is largely determined during postheading. Hence, agronomically, it is convenient to regard the life history of rice in terms of three growth stages: vegetative, reproductive, and ripening. The vegetative stage refers to a period from germination to the initiation of panicle primordia; the reproductive stage, from panicle primordia initiation to heading; and the ripening period, from heading to maturity (Fig. 1.1). A 120-day variety, when planted in a tropical environment, spends about 60 days in the vegetative stage, 30 days in the reproductive stage, and 30 days in the ripening period.