absolute long-day plants (qualitative long-day plants, obligatory long-day plants)：The plants whose flowering absolutely depends on a long-day condition. They flower only under long-day conditions, and never flower under unsuitable photoperiodic cycle conditions. Antonym is "facultative long-day plants". absolute response (qualitative response, obligatory response)：The plants whose flowering absolutely depends on the photoperiodic cycle condition or low temperature. They never flower under unsuitable photoperiodic cycles or temperature conditions. Antonym is "facultative response". absolute short-day plants (qualitative short-day plants, obligatory short-day plants)：The plants whose flowering absolutely depends on short-day conditions. They flower only under short-day conditions, and never flower under unsuitable photoperiodic cycle conditions. Antonym is "facultative response short-day plants". ambiphotoperiodic plants：The plants which flower only under photoperiods shorter than a certain length or longer than another certain length. An example is Madia elegans which flowers under photoperiods shorter than 14 hours or longer than 18 hours. This type of plant is quite rare. anthesin：An assumed flower-inducing substance. M.Kh.Chailakyan proposed that florigen consisted of gibberellins and anthesin. This theory is mostly ignored today. bolting：The process by which rosette plants elongate their stems. It occurs when flowering is induced in long-day plants or cold-requiring plants. However, bolting is not the same as flowering. Sometimes, the stem would elongate but flower buds would not be formed. cold-requiring plants：The plants which are induced to flower when exposed to low temperatures. critical dark period (critical nightlength, critical night)：The length of night or dark period in a 24-hour cycle required to inhibit flowering of long-day plants or to induce flowering of short-day plants. When the length of night is longer than the critical dark period, short-day plants are induced to flower and long-day plants never flower. In a natural setting, critical dark period is 24 hours minus critical daylength. Since the factor regulating photoperiodic flowering is not daylength but nightlength, the critical dark period rather than critical daylength should be referred to. "Nightlength" is also spelled "night length". critical day： The same as "critical daylength". critical daylength (critical day, critical photoperiod)：The length of day or light period in a 24-hour cycle required to induce flowering of long-day plants or to inhibit flowering of short-day plants. When the day length is longer than the critical daylength, long-day plants are induced to flower and short-day plants never flower. critical night： The same as "critical dark period". critical nightlength： The same as "critical dark period". critical photoperiod： The same as "critical daylength". daylength： The same as "photoperiod". Also spelled "day length". day-neutral plants：The plants whose flowering does not depend on nightlength. The flowering of day-neutral plants is triggered when plants reach a certain age. devernalization：The reversal of the effect of an inductive low temperature in vernalization by exposure to high temperatures. facultative long-day plants (quantitative long-day plants)：The plants whose flowering is promoted by a long-day condition. They can flower even under inappropriate photoperiods, although flowering is delayed. Antonym is "absolute long-day plants". facultative response (quantitative response)：The response which is promoted by a suitable condition. The response could occur even under an inappropriate condition, although it is delayed. Antonym is "absolute response". facultative short-day plants (quantitative short-day plants)：The plants whose flowering is promoted by a short-day condition. They can flower even under inappropriate photoperiods, although flowering is delayed. Antonym is "absolute short-day plants". floral evocation：The process committing the shoot apical meristem irreversibly to form floral bud primordia in response to the flowering stimulus. florigen (flowering hormone)：A chemical substance proposed by Chailakhyan (1937) as a flowering stimulus which is generated in the leaf after perception of an appropriate photoperiodic signal. It is transmitted to the shoot apical meristem where floral evocation occurrs. flower formation： The same as "flowering". flower-inducing substance：Any substance inducing flowering. In a strict sense, a substance transmitted from the photoinduced leaf to the shoot apical meristem resulting in floral evocation. Also substances which induce flowering when applied to the plant. The natural flower-inducing substance generated under an appropriate photoperiod is called florigen. flower induction (floral induction, flower initiation)：The process where the leaf generates a flowering stimulus in response to appropriate photoperiods. flower initiation (floral initiation)： The same as "flower induction". flowering (flower formation)：The change from vegetative growth to reproductive growth. Refers to the whole process from the flower induction to the floral evocation. The term "anthogenesis" is not used today. "Flower opening" is a different phenomenon which occurs after the process of flowering is completed. flowering hormone：The same as "florigen". flowering stimulus (floral stimulus)：A factor which is generated in the leaf exposed to an appropriate photoperiod. It is transmitted to the shoot apical meristem and induces the floral evocation. Florigen is proposed as a flowering stimulus. inductive photoperiod：The photoperiod under which flowering is induced. intermediate-day plants：The plants which flower when the dark length is a certain length. An example is Salsola komarovii which flowers when nightlength is around 12 hours. Flowering is delayed under both longer and shorter nightlengths. This type of plant is quite rare. The intermediate-day plant is a modification of a short-day plant. long-day condition：The photoperiod where the daylength is longer than the critical daylength (the dark length is shorter than the critical dark length). Under this condition, long-day plants are induced to flower and short-day plants are not induced to flower. In many experiments, daily cycles of 16 hours light and 8 hours darkness are used as the long-day condition, under which almost all long-day plants are induced to flower while almost all short-day plants are not induced to flower. long-day plants：The plants which flower under dark period shorter than the critical night length (light period longer than the critical day length). long-short-day plants：The plants which flower when placed under long-day conditions and then under short-day conditions. multifactorial theory：The theory that flowering is not induced by a specific substance such as florigen but that it occurs in the presence of multiple factors such as sucrose, calcium ion, polyamines, and cytokinins. night interruption： The same as "night break". night break (night interruption)：A brief irradiation inserted in the dark period which cancels the effect of darkness. A night break given during a dark period longer than the critical dark length inhibits flowering of short-day plants and promotes flowering of long-day plants. obligatory long-day plants： The same as "absolute long-day plants". obligatory response： The same as "absolute response". obligatory short-day plants： The same as "absolute short-day plants". photoperiod (daylength)：The length of day (light period) in the daily cycle. photoperiodic cycle：The cycling of day and night (light and darkness) . photoperiodic flowering：The flowering which occurs in response to the photoperiodic cycle. photoperiodism：The nature which plant responds to photoperiodic cycle such as flowering. qualitative long-day plants： The same as "absolute long-day plants". qualitative response： The same as "absolute response". qualitative short-day plants： The same as "absolute short-day plants". quantitative long-day plants： The same as "facultative long-day plants". quantitative response： The same as "facultative response". quantitative short-day plants： The same as "facultative short-day plants". rosette：A form of plant whose stem elongation is restricted in the vegetative growth phase. Many leaves are attached to a short stem, and therefore the plant has the appearance of a rose flower. short-day condition：The photoperiodic condition where short-day plants are induced to flower and long-day plants are not induced to flower. In many experiments, a daily cycle of 8 hours light and 16 hours darkness is used as the short-day condition, under which almost all short-day plants are induced to flower and almost all long-day plants are not induced to flower. short-day plants：Plants which flower when exposed to a dark period longer than the critical length (light period shorter than the critical length). stress-induced flowering：The flowering which is induced by stress factors such as low temperature (around 15 ℃), poor nutrition, and high intensity light. Known in Pharbitis nil, Perilla frutescens and Lemna spp. short-long-day plants：The plants which flower when placed under short-day conditions and then under long-day conditions. vernalin：The flower-inducing substance proposed to be generated by vernalization separate from florigen. It has not been substantiated. vernalization：The flowering induced by low temperature (0 to 5 ℃). Also the promotive effects of low temperatures on flowering. Sometimes spelled "vernalisation".