We have known for a long time that flowers of different plants open and close at different times of a day. Yet no one really understands why flowers open and close like that at special times. The question is not as simple as we might think, as recent experiments have shown. In one experiment, flowers were kept in complete darkness all the time. We might expect that the flowers, without any information about the day, did not open as they usually do. In fact, they continued to open at the usual time. This has shown that they have some special ways of knowing the time.

    Their sense of time does not depend on the information from the outside world. It is inside them a kind of "inner clock". This discovery may not seem to be very important. However, it is later found that not just plants but animals including man have this "inner clock" which controls the working of their bodies and influences their activities. Human beings, then, are also influenced by the mysterious power. Whether we wish or not, it affects such things in our life as our need for sleep or food.