Overview of the control of flowering time
Some plants initiate flowering regardless of their environment, showing an autonomous flowering response, whereas others will only flower when environmental requirements are met, showing an obligate/qualitative response to their environment. Many plants are strongly influenced by environmental factors, but will also make the transition to flowering if these stimuli are not received after a pre-determined period of growth, and are said to show a facultative/quantitative response to their environment.
Many environmental factors, such as stress and nutrient availability, influence flowering time, but perhaps the most important are light and temperature. With regards to light the quantity, quality and duration (photoperiod) are all important variables. During the control of flowering photoperiod and temperature are perceived in different parts of the plant. Photoperiod is perceived in the leaves, whereas vernalisation (a prolonged exposure to low temperatures; see section 1.2.1.4) is perceived in the shoot apex (Lang, 1965; Zeevaart and Boyer, 1987) .
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