The soil seed bank consists of numerous seeds, many of which are dormant and delay germination until a later time. The persistent portion of the soil seed bank is a major source of future plants. Certain plant species emerge during the same season of each year. This is mainly due to seed germination responses to the seasonal soil temperature cycles. For example, seeds of summer annuals germinate when soil temperatures are rising after a winter season, and winter annuals germinate while soil temperatures are moderate following a summer season. As a result of dormancy cycling, germination is limited to the season coinciding with the phase of low dormancy in the cycle. Temperature strongly influences physiological and biochemical processes. Decomposed plant materials, mainly phenolics, are known to inhibit seed germination. Nitrate has received considerable attention as a possible regulator of seed germination in soil. Seed dormancy increases the chances for perpetuation of annual plants in a sometimes hazardous environment.