photoperiodism defined in 1951 yearphotoperiodism - photoperiodism;
photoperiodism - Response of plants to relative length of day and night. Although flowering display is best known example of photoperiodism many other plant responses are controlled by photoperiod. Photoperiodic responses are regulated by the photo-reversible pigment phytochrome. Gircadian rhythms are considered to be a fundamental basis of photoperiodism. Short-day plants, e.g. chrysanthemum, cosmos, soybean, usually flower only in response to photoperiods (day lengths) that are shorter than a certain critical length in each 24-hour cycle, i.e. they respond inductively to a 'long night'. In contrast to these are long-day plants, e.g. radish, lettuce, henbane, that usually flower only in response to photoperiods that are longer than a certain critical level in each 24-hour cycle, i.e. they respond inductively to a 'short-night'. All gradations between short and long-day types exist; in some, day-neutral plants, e.g. tomato, flowering is virtually unaffected by photoperiod. Photoperiodic response varies with age of plant and with temperature. The photoperiodic stimulus is perceived by leaves and is transmitted, probably in form of a hormone (tentatively named florigen) to growing points where it induces flower initiation. Similar effects of day-length regulate the timing of the breeding season in many vertebrate animals.
near photoperiodism in Knolik
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