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Foxy tale
The last word– CLOSING TIME Why do some flowers close at night? What is the evolutionary advantage of doing this, and why do only some plants bother to do so?
● When flowers close temporarily for the night they are effectively in standby mode, protecting their delicate reproductive parts and pollen while they are not in use. The pollen is isolated from the dew that forms during the night, keeping it dry so that it can be dusted onto a passing insect the following day. Indeed, some flowers remain closed until some time after dawn, and only reopen when the day is warm enough for the dew to have evaporated. Closing the flowers also helps to protect against night-time cold and bad weather. As well as closing their petals, some plants also close the tough surrounding structures, called bracts, to protect the flower against plant-eating insects. Keeping the pollen dry while limiting access for plant-eating insects – and the fungi and bacteria that they carry – also means that the pollen is less likely to spoil. Ultimately all these adaptations minimise wastage of pollen or damage to the flower. This kind of economy is a particular advantage for plants that live in what might be termed stressful environments with limited resources, where they would be hard-pressed to produce new flowers and so must protect their existing investment. Species that have evolved to make the most of lusher habitats in which more Questions and answers should be kept as concise as possible. We reserve the right to edit items for clarity and style. Please include a daytime telephone number and email address if you have one. Questions should be restricted to scientific enquiries about everyday phenomena. The writers of all published answers will receive a cheque for £25 (or the US$ equivalent). Reed Business Information Ltd reserves all rights to reuse question and answer material submitted by
resources are available are not so frugal: their strategy is to produce fresh flowers when needed rather than maintaining, and closing, the ones they already have. Some plants have adapted the movements of their flowers to odd ecological situations. For example, certain bat-pollinated wild pineapples, members of the bromeliad family, do the exact opposite of most flowers by opening their flowers at night and closing them during the day to protect them from weevils, which are most active during daylight hours. The mechanisms that flowers use to close their petals are essentially the same as the ones they use to open out in the first place, and are not the same in all species. Those of the Kalanchoe genus open their flowers by growing new cells on the inner surface of the petals to force them outwards, and on the outside of the petals to close them. Gentian flowers
“Some flowers open and close so punctually that a once-popular gardening fashion was to plant flowers in sectors of a bed resembling a clock face” use the expansion and contraction of the cells that form the petal. This type of movement is controlled by genes that switch on or off in response to changes in temperature or the amount of light, and are regulated by an internal clock. The genes regulate the amount of sugars in the petal cell sap: larger amounts cause water to readers in any medium or format. Send questions and answers to The Last Word, New Scientist, Lacon House, 84 Theobald’s Road, London WC1X 8NS, UK (fax +44 (0) 20 7611 1280), by email to [email protected] or visit www. newscientist.com/lastword.ns (please include a postal address in order to receive payment for answers). If you would like a list of all unanswered questions please send an SAE to LWQlist at the above address.
Memorable answer? The Last Word and New Scientist have teamed up with Crucial Technology (www.crucial.com/uk) and will be awarding each successful author a 512MB Gizmo! overdrive.
Last Words past and present, plus a full list of unanswered questions, are available at www.newscientist.com
enter the petals by osmosis, pressurising them and opening the flower. In effect, when these flowers close they do so by wilting. Simon Pierce University of Insubria, Varese, Italy ● There are a number of reasons for the differing approaches of various flower types. Long-blooming flowers close and reopen repeatedly, whereas other flowers may drop their petals after a single day. Long-lasting flower heads of many members of the Asteraceae family, for example, and flowers of some members of the genus Mesembryanthemum (their very name means “midday flowering”) protect their gonads from night-time dews or frosts but open in sunlight. Where sun, dew, frost, wind or insects are likely to damage exposed reproductive organs, closing may be advantageous during times when flowers are unlikely to attract pollinators. Analogously, many moth-pollinated flowers release their fragrance only at night, so avoiding waste during daylight. Some flowers open and close so punctually that a once-popular gardening fashion was to plant flowers in sectors of a bed resembling a clock face. These were so planned that flowers opening in each sector matched the position of a notional hour hand on the clock. In season, all being well, one might actually be able to tell the time by consulting one’s flowering clock. Of course, such non-overlapping timed opening reduces competition for pollinators, and bees soon learn to concentrate on the most rewarding plants at the times when they open
reliably. Arbitrarily visiting assorted flowers would be less efficient for both the bee and the plant, increasing the wastage of pollen on unrelated plants. Jon Richfield Somerset West, South Africa
THIS WEEK’S QUESTIONS Foxy tale From a slow-moving train I saw a fox standing with its tail resting on the ground while two magpies repeatedly took turns to peck the tip of the tail, before running off. The fox merely flicked its tail each time. What were they all doing? Sue Murdochs Marton cum Grafton, North Yorkshire, UK Distributory dilemma When great ice fields melt, will any resulting rise in sea level be equal at all latitudes, or will the Earth’s rotation make it greater at the equator? If there is a difference, has this been factored in when discussing the effect of melting ice sheets? By email, no name or address supplied Kitchen lottery I make the batter for my Yorkshire pudding to exactly the same recipe each week, yet sometimes it rises in the oven while at other times it doesn’t. What properties of batter, or what unnoticed change in my cooking technique or my oven could be behind this weekly lottery? Janice Bentley Leeds, West Yorkshire, UK
WHY DON’T PENGUINS’ FEET FREEZE? The latest collection from The Last Word, answering some of the world’s most baffling questions Available in bookstores and online at www.newscientist.com/lastword3.ns
● When flowers close temporarily for the night they are effectively in standby mode, protecting their delicate reproductive parts and pollen while they are not in use. The pollen is isolated from the dew that forms during the night, keeping it dry so that it can be dusted onto a passing insect the following day. Indeed, some flowers remain closed until some time after dawn, and only reopen when the day is warm enough for the dew to have evaporated. Closing the flowers also helps to protect against night-time cold and bad weather. As well as closing their petals, some plants also close the tough surrounding structures, called bracts, to protect the flower against plant-eating insects. Keeping the pollen dry while limiting access for plant-eating insects – and the fungi and bacteria that they carry – also means that the pollen is less likely to spoil. Ultimately all these adaptations minimise wastage of pollen or damage to the flower. This kind of economy is a particular advantage for plants that live in what might be termed stressful environments with limited resources, where they would be hard-pressed to produce new flowers and so must protect their existing investment. Species that have evolved to make the most of lusher habitats in which more Questions and answers should be kept as concise as possible. We reserve the right to edit items for clarity and style. Please include a daytime telephone number and email address if you have one. Questions should be restricted to scientific enquiries about everyday phenomena. The writers of all published answers will receive a cheque for £25 (or the US$ equivalent). Reed Business Information Ltd reserves all rights to reuse question and answer material submitted by
resources are available are not so frugal: their strategy is to produce fresh flowers when needed rather than maintaining, and closing, the ones they already have. Some plants have adapted the movements of their flowers to odd ecological situations. For example, certain bat-pollinated wild pineapples, members of the bromeliad family, do the exact opposite of most flowers by opening their flowers at night and closing them during the day to protect them from weevils, which are most active during daylight hours. The mechanisms that flowers use to close their petals are essentially the same as the ones they use to open out in the first place, and are not the same in all species. Those of the Kalanchoe genus open their flowers by growing new cells on the inner surface of the petals to force them outwards, and on the outside of the petals to close them. Gentian flowers
“Some flowers open and close so punctually that a once-popular gardening fashion was to plant flowers in sectors of a bed resembling a clock face” use the expansion and contraction of the cells that form the petal. This type of movement is controlled by genes that switch on or off in response to changes in temperature or the amount of light, and are regulated by an internal clock. The genes regulate the amount of sugars in the petal cell sap: larger amounts cause water to readers in any medium or format. Send questions and answers to The Last Word, New Scientist, Lacon House, 84 Theobald’s Road, London WC1X 8NS, UK (fax +44 (0) 20 7611 1280), by email to [email protected] or visit www. newscientist.com/lastword.ns (please include a postal address in order to receive payment for answers). If you would like a list of all unanswered questions please send an SAE to LWQlist at the above address.
Memorable answer? The Last Word and New Scientist have teamed up with Crucial Technology (www.crucial.com/uk) and will be awarding each successful author a 512MB Gizmo! overdrive.
Last Words past and present, plus a full list of unanswered questions, are available at www.newscientist.com
enter the petals by osmosis, pressurising them and opening the flower. In effect, when these flowers close they do so by wilting. Simon Pierce University of Insubria, Varese, Italy ● There are a number of reasons for the differing approaches of various flower types. Long-blooming flowers close and reopen repeatedly, whereas other flowers may drop their petals after a single day. Long-lasting flower heads of many members of the Asteraceae family, for example, and flowers of some members of the genus Mesembryanthemum (their very name means “midday flowering”) protect their gonads from night-time dews or frosts but open in sunlight. Where sun, dew, frost, wind or insects are likely to damage exposed reproductive organs, closing may be advantageous during times when flowers are unlikely to attract pollinators. Analogously, many moth-pollinated flowers release their fragrance only at night, so avoiding waste during daylight. Some flowers open and close so punctually that a once-popular gardening fashion was to plant flowers in sectors of a bed resembling a clock face. These were so planned that flowers opening in each sector matched the position of a notional hour hand on the clock. In season, all being well, one might actually be able to tell the time by consulting one’s flowering clock. Of course, such non-overlapping timed opening reduces competition for pollinators, and bees soon learn to concentrate on the most rewarding plants at the times when they open
reliably. Arbitrarily visiting assorted flowers would be less efficient for both the bee and the plant, increasing the wastage of pollen on unrelated plants. Jon Richfield Somerset West, South Africa
THIS WEEK’S QUESTIONS Foxy tale From a slow-moving train I saw a fox standing with its tail resting on the ground while two magpies repeatedly took turns to peck the tip of the tail, before running off. The fox merely flicked its tail each time. What were they all doing? Sue Murdochs Marton cum Grafton, North Yorkshire, UK Distributory dilemma When great ice fields melt, will any resulting rise in sea level be equal at all latitudes, or will the Earth’s rotation make it greater at the equator? If there is a difference, has this been factored in when discussing the effect of melting ice sheets? By email, no name or address supplied Kitchen lottery I make the batter for my Yorkshire pudding to exactly the same recipe each week, yet sometimes it rises in the oven while at other times it doesn’t. What properties of batter, or what unnoticed change in my cooking technique or my oven could be behind this weekly lottery? Janice Bentley Leeds, West Yorkshire, UK
WHY DON’T PENGUINS’ FEET FREEZE? The latest collection from The Last Word, answering some of the world’s most baffling questions Available in bookstores and online at www.newscientist.com/lastword3.ns