本世纪二十年代初,科学工作者在研究烟草新品种时,偶然发现有一种烟革不象别的品种那样在夏季开花,而是在冬季移入温室后才开花。倘若在夏季人为地缩短日照长度,这种烟草也能开花,相反冬季在温室内人工延长光照,它便保持营养生长而一直不能开花。他们还发现,从5～7月每隔两周播种一次大豆,尽管植株生长的“年龄”不同,但到了秋天(9月份)几乎同时开花。这是为什么呢?原来,这种烟草和大豆,只有在光照缩短到一定程度后,才开始开花。这说明,自然环境中光照与黑暗 In the early 1920s, when scientists studied new varieties of tobacco, they occasionally discovered that one type of tobacco did not bloom in the summer as in other varieties, but bloomed after it was transferred to the greenhouse in winter. If artificially shortening the length of the sunshine during the summer, the tobacco is also able to flowering. On the contrary, in winter, artificial lighting is prolonged in the greenhouse, and it grows vegetatively and never blooms. They also found that sowing soybeans every two weeks from May to July led to almost the same flowering in the fall (September) despite the “age” of plant growth. Why is this? Originally, this tobacco and soybeans, only to a certain extent after the light shortened, began to bloom. This shows that light and darkness in the natural environment