Steve Piper, age 10, of St. Paul, Minnesota, for his question:
How does the morning sun open the flowers?
The crocus closes its papery petals at night and opens to greet the morning sun. So do waxy water lilies, golden dandelions and many other flowers. But the climbing morning glory closes its sky blue trumpets soon after sunrise. And out in the meadows of wild flowers, the evening primrose closes all day and opens its dainty blossoms as the sun sinks to bed. The sun helps flowers to open and close, but so do air, temperature and moisture.
The generous planet seems to have everything except simple answers to our questions. It puts forth thousands of different flowers. Surely we can expect a simple answer to how and why these blossoms open and close their petals. Not so. The secret operations go on inside living cells. It takes about 4,000 of them to measure an inch. But we can imagine part of this operation if we think of 4,000 balloons.
When the balloons are empty, we can pack them in a trunk. But puffed up with air, they can fill a big room. If the room were a big balloon, it would collapse around the empty little balloons and expand to its full size when they filled with air. This is somewhat like the operation that takes place when flower petals open and close. When their tiny cells lose moisture, the petals sag or neatly fold and close the flower. When all the cells are full of moisture, they balloon up and make the petals stiff. The stiff petals spread out and the flower opens.
This may seem rather simple, but it is linked~to some very complex operations both inside and outside the plant. It depends on the plumbing system that totes moisture from the roots to the topmost edges of the plant. It is related to how plants breathe without noses or lungs and how they lose water vapor through special pores in their leaves and petals. These inside operations work with the air, temperature and sunshine outside the plant. The complete answer is very, very complicated. Besides, it is tricky because different flowers react to sunshine and warmth in different ways.
The golden dandelion opens up wide to enjoy the warm sunshine. But its petals cannot remain firm in the cool night air. After sunset, they lose some of their moisture and the flower sags closed. In the early morning, two things happen to fill the petal cells with moisture again. There is a short surge of moisture from the roots, up through the plumbing system.
Meantime, the morning sun warms the air and warm air is thirsty. It takes water vapor from the pores in the petals. But as the surface cells lose moisture, they pull more from neighboring cells. They keep supplies of water streaming up through the plant. The moisture filled petals stay stiff and hold the flower open as long as the warm sun evaporates moisture from their pores. However, other factors help or hinder the complex operation.
Other flowers react to warmth and sunshine in different ways. The sunflower turns its heavy head to face the sun all day. Most daisies love sunshine and also stay open during the cooler nights. But the morning glory can stand only a few hours of warm, morning sunshine. The daytime sun is too much for the evening primrose, so it opens its petals at twilight.