ChatterBank2 mins ago
Seasons
4 Answers
Hi all, often wondered this but anyone know why plants/flowers etc bloom according to season? Sounds a silly question I know but why should a daffodil flower in Spring and not Summer? What if someone was able to keep their garden at the same temperature for a whole year or more? Would that make any difference to when strawberries ripened or stop leaves turning yellow and falling in Autumn?
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An article from my collection of Scientific Amercan entitled "LIfe Processes of Plants by A. W. Galston addresses your specific question: (Take a deep breath and relax).
"The process to which your question refers is called photoperiodism. How day length affects the flowering of some, but not all plants
Around 1920 Garner and Allard, working on tobacco plants at an USDA experimental station, discovered some very large plants with enormous leaves among a batch of seed they were raising.
They looked forward to collecting the seed with a view to developing a strain. However, whilst the normal tobacco plants set seed in late summer, the large form showed no sign of flowering. They therefore dug them up and transferred them to a greenhouse, where the plants eventually flowered in late December. The progeny of these plants exhibited the same characteristic of late flowering.
Garner and Allard experimented moving the plants from a darkhouse to a greenhouse on a daily basis and determined that these plants flowered with the combination of 9 hours daylight and 15 hours darkness, which is characteristic for Maryland’s latitude in late December.
At this point one should remember that latitude governs difference in day length. At the equator days and nights are of an equal length. The further one gets from the equator, the greater the difference in daylength.
Garner and Allard later determined that soya likewise flowers after exposure to a certain number of consecutive short days. Spinach and most cereals, however, responded to long days. Whilst some other plants, like tomato, are unaffected by day length and flower once they have reached a certain size or developed a particular number of leaves.
They named this response of plants to relative lengths of day and night photoperiodism, and classified plants as short-day, long-day and day-neutral
(Contd.)
"The process to which your question refers is called photoperiodism. How day length affects the flowering of some, but not all plants
Around 1920 Garner and Allard, working on tobacco plants at an USDA experimental station, discovered some very large plants with enormous leaves among a batch of seed they were raising.
They looked forward to collecting the seed with a view to developing a strain. However, whilst the normal tobacco plants set seed in late summer, the large form showed no sign of flowering. They therefore dug them up and transferred them to a greenhouse, where the plants eventually flowered in late December. The progeny of these plants exhibited the same characteristic of late flowering.
Garner and Allard experimented moving the plants from a darkhouse to a greenhouse on a daily basis and determined that these plants flowered with the combination of 9 hours daylight and 15 hours darkness, which is characteristic for Maryland’s latitude in late December.
At this point one should remember that latitude governs difference in day length. At the equator days and nights are of an equal length. The further one gets from the equator, the greater the difference in daylength.
Garner and Allard later determined that soya likewise flowers after exposure to a certain number of consecutive short days. Spinach and most cereals, however, responded to long days. Whilst some other plants, like tomato, are unaffected by day length and flower once they have reached a certain size or developed a particular number of leaves.
They named this response of plants to relative lengths of day and night photoperiodism, and classified plants as short-day, long-day and day-neutral
(Contd.)
(Contd.
It has subsequently been shown that plants do not measure daylength but night length. Thus short day plants can be inhibited from flowering by administering a brief flash of light during the night. Although the plants are measuring night length rather than daylight, the term photoperiodism has been retained.
The extent to which plants can determine precise daylengths is extraordinary.
Some genera can perceive a difference of between 2-5 minutes. Likewise the number of consecutive days of a particular length can be as low as 1-4.
The change that occurs as a result of these daylengths being reached, is the shoot tip changes from normal vegetative growth, to producing a flowering bud.
The daylength at which the change from vegetative to flowering state occurs is known as the critical photoperiod.
Note that short-day plants initiate flowerbuds when the daylength is less than the critical period while long-day plants initiate flower buds when the daylength is greater than the critical period.
It is not the absolute length of day which is important in determining whether a plant is short or long day. A long-day plant flowering in early spring (black henbane) will have a critical period several hours shorter than a short-day plant flowering just after mid-summer (cocklebur)."
It has subsequently been shown that plants do not measure daylength but night length. Thus short day plants can be inhibited from flowering by administering a brief flash of light during the night. Although the plants are measuring night length rather than daylight, the term photoperiodism has been retained.
The extent to which plants can determine precise daylengths is extraordinary.
Some genera can perceive a difference of between 2-5 minutes. Likewise the number of consecutive days of a particular length can be as low as 1-4.
The change that occurs as a result of these daylengths being reached, is the shoot tip changes from normal vegetative growth, to producing a flowering bud.
The daylength at which the change from vegetative to flowering state occurs is known as the critical photoperiod.
Note that short-day plants initiate flowerbuds when the daylength is less than the critical period while long-day plants initiate flower buds when the daylength is greater than the critical period.
It is not the absolute length of day which is important in determining whether a plant is short or long day. A long-day plant flowering in early spring (black henbane) will have a critical period several hours shorter than a short-day plant flowering just after mid-summer (cocklebur)."
In temperate climates there are not many insects about in the cold weather so most plants wait until warmer weather to flower so the flowers can be pollinated. Yes, bulbs also propagate via flower seed to remain a true species.
The daylight length sensitivity (as explain so proficiently by clanad above) occurs in animals as well as plants.
The daylight length sensitivity (as explain so proficiently by clanad above) occurs in animals as well as plants.
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