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  • 植物适应

    Close-up of pink flowers of a Christmas cactus against green foliage.

    How does this plant know it's Christmas?
    ::这植物怎么知道是圣诞节?

    This plant is known as a Christmas cactus because it only blooms once a year, during the Christmas season. But plants can't read a calendar. How can a houseplant know the time of the year?
    ::这个植物被称为圣诞仙人掌, 因为它每年只在圣诞节季节开花一次。 但是植物不能阅读日历。 家庭植物怎么会知道一年的时间呢 ?

    Seasonal Changes
    ::季节变化

    Have you seen the leaves of plants change colors? During what time of year does this happen? What causes it to happen? Plants can sense changes in the seasons . Leaves change color and drop each autumn in some climates ( Figure ).
    ::你见过植物的叶子改变颜色吗?这种变化是在哪一年发生的?是什么原因?植物能感觉到季节的变化。叶子会改变颜色,并且在某些气候中每年秋天都会下降(图 ) 。

    Autumn leaves in vibrant orange and yellow against a clear blue sky.

    Leaves changing color is a response to the shortened length of the day in autumn.
    ::变换颜色的叶子是秋天白天缩短的一种反应。

    Certain flowers , like poinsettias, only bloom during the winter. And, in the spring, the winter buds on the trees break open, and the leaves start to grow. How do plants detect time of year?
    ::某些花朵,如花朵,只有在冬天才开花。在春天,树上的冬芽断开,树叶开始生长。植物如何测出一年的时间?

    Although you might detect seasonal changes by the change in temperature, this is not the way in which plants know the seasons are changing. Plants determine the time of year by the length of daylight, known as the photoperiod. Because of the tilt of the Earth, during winter days, there are less hours of light than during summer days. That’s why, in the winter, it starts getting dark very early in the evening, and then stays dark while you’re getting ready for school the next morning. But in the summer it will be bright early in the morning, and the sun will not set until late that night. With a light-sensitive chemical, plants can sense the differences in day length.
    ::尽管您可能通过温度变化来检测季节性变化,但这并不是植物知道季节变化的方式。植物根据白天的时间来决定一年的时间,也就是光亮期。由于地球的倾斜,冬季的光亮时间比夏季的亮度少。 这就是为什么冬天在晚上很早开始黑暗,然后在第二天早上准备上学的时候保持黑暗。 但在夏天,清晨的亮度会很亮,太阳不会落到那个晚上的深夜。 有了一种对光敏感的化学物质,植物可以感觉到白天的差别。

    For example, in the fall, when the days start to get shorter, the trees sense that there is less sunlight. The plant is stimulated, and it sends messages telling the leaves to change colors and fall. This is an example of photoperiodism , the reaction of organisms , such as plants, to the length of day or night. Photoperiodism is also the reaction of plants to the length of light and dark periods. Many flowering plants sense the length of night, a dark period, as a signal to flower. Each plant has a different photoperiod, or night length. When the plant senses the appropriate length of darkness, resulting in an appropriate length of daylight, it flowers. Flowering plants are classified as long-day plants or short-day plants. Long-day plants flower when the length of daylight exceeds the necessary photoperiod, and short-day plants flower when the day length is shorter than the necessary photoperiod. Long-day plants include carnations, clover, lettuce, wheat, and turnips. Short-day plants include cotton, rice, and sugar cane.
    ::例如,在秋天,当白天开始变短时,树就感觉到阳光越来越少。植物被刺激,发出信息告诉叶子以改变颜色和落叶。这是光时期、植物等生物对白天或夜间的反应的例子。光时期也是植物对光长和黑暗时期的反应。许多花卉植物感觉到黑夜的长度,黑暗时期,作为花朵的信号。每个植物有不同的照相期或黑夜长度。当植物感知适当的黑暗时间,导致适当的日光长度时,植物就会花花朵。花朵被归类为长天植物或短天植物。白天长度超过必要的光期的植物会花朵,白天短天植物会花花花花,白天短时间的植物会比必要的光期短。长的植物包括康奈、凝胶、生菜、小麦和小菜。短天植物包括棉花、大米和甘蔗。

    Summary
    ::摘要

    • Plants can respond to the change of season by losing their leaves, flowering, or breaking dormancy.
      ::植物可以通过失去叶子、开花或断绝宿舍来应对季节的变化。
    • Plants go through seasonal changes after detecting differences in day length.
      ::植物在发现白天长度差异后经历了季节性变化。

    Explore More
    ::探索更多

    Use the resource below to answer the questions that follow.
    ::利用以下资源回答以下问题。

    • Why Do Leaves Change Color? at  .
      ::为什么叶子换颜色?
    1. Where does leaf color come from?
      ::叶子颜色从哪里来的?
    2. How do leaves change color?
      ::叶子如何改变颜色?
    3. Do leaves change color because of weather?
      ::叶子是否因为天气而改变颜色?
    4. How does temperature affect the color of the leaves?
      ::温度如何影响叶子的颜色?
    5. Why do leaves fall?
      ::为什么叶子掉下来?

    Review
    ::回顾

    1. How do plants detect the change in seasons?
      ::植物如何检测季节变化?
    2. What signals a tree to drop its leaves?
      ::树的树叶会掉落什么?
    3. Distinguish between long-day plants and short-day plants.
      ::区分长日植物和短日植物。
    4. Give two examples of long-day plants.
      ::举两个长日植物的例子。