从向日葵谈起早晨,向日葵总是迎着初升的朝阳;傍晚,它又送夕阳下山。为什么向日葵总是向着太阳呢?据科学家研究,原来向日葵的茎顶端有一种物质,叫生长素。这种物质能够促进植物生长,但是它又有些怕光,总是躲在向日葵的背面;于是,向日葵背光的一面生长素含量就比较高,向光的一面含量比较低。这样一来,背光的一面生长较快,向光的一面生长较慢,所以向日葵的顶部总是跟着太阳转。生长素对于植物,就象激素(荷尔蒙)对于动物一样。因此它被称为植物激素,或者更恰当地说,它是植物激素之一。目前发现的普遍存在于植物中的生长素是吲 From the morning of sunflowers, sunflowers are always facing the rising sun. In the evening, they send sunsets. Why is the sunflower always facing the sun? According to scientists, the original sunflower stem has a substance called auxin. This substance can promote plant growth, but it is also a bit afraid of light, and it is always hidden behind the sunflower. Therefore, sunflower has a high level of auxin on one side of the backlight and a lower content on the side of the light. As a result, one side of the backlight grows faster and grows slower toward the light side, so the top of the sunflower always follows the sun. Auxin is like a hormone (hormone) to an animal. It is therefore called a plant hormone or, more properly, it is one of the plant hormones. The auxins commonly found in plants today are