LESSON XIV.
PLANT CLOCKS.
I knew an old man who made a great clock for his grandchildren. What kind of a clock do you suppose it was? The clock was in the garden, and it was made of flowers.
Did it tell the time well? Only pretty well. Flower clocks are as liable to get out of order as clocks made at a factory.
This clock was a great flower bed, divided into twelve parts. The divisions were marked out by little rows of box-plants. In the middle was a post three feet high. It had two clock hands on it, buttheywere only for show. They did not move.
But the post had a sun-dial on it, and that gave true time. So the children could tell when the flower clock was not working well.
As there are twelve hours of day and twelve of night,and some plants open only at night, each of the twelve divisions of the clock was divided into two parts by a little line of red colors. On one side of this were the night bloomers, on the other side the day bloomers.
The children thought it lovely, and were proud of it. And the clock did for them what the grandfather wished,—it made them like and notice plants.
I have just said that there are plants which open only by night, and others which open only by day. This opening and shutting for day and night is called “the sleep of plants.”
This sleep of plants is not because the plant is tired; it is due to the absence or presence of light, and to changes in the amount of light. Yet, no doubt, in it the organs of the plant do rest, as their growth and action are not then so rapid.
Both the flowers and the leaves of plants have this sleep motion. We will look first at the sleep of flowers.
You have noticed that the morning-glories are open when you rise, and that they fold or shut up by noon. Have you in your garden a flower with gay yellow or scarlet blossoms, called the four-o’clock? That does not open until about four in the afternoon.
As you run to school in the morning, the dandelions are gay along the way-side. When you come from school in the afternoon, the dandelions are all folded in their green cups.
If this is so, why does not the flower-clock tell true time? You can see that owing to the changes in the heat and rising of the sun in different places, and seasons, the sleep of the flowers would not begin at the same time.
I have seen my morning-glories open as late as nine o’clock, and stay open all day in cool October days. In August they opened by six and were shut by eleven. So the four-o’clocks and dandelions may vary by an hour or two.
All the water-lilies shut at night. Some not only shut, but draw their heads down under water. I will tell you when you will find some flowers opening. At four in the morning you will find the goat’s-beard and the blue chicory opening. The chicory petals are then a fine blue. They become lighter in color until near mid-day, when they are almost white. Chicory is called “Miss-go-to-bed-at-noon” by some children, as the flowers shut at noon.
At five in the morning the common morning-glory and the poppy open. At six the yellow hawk’s-weedand dandelions look out on the way-side. At seven the water-lilies smile at us. At eight, if the day is fine, the pimpernel opens its red eyes.
At nine the marigold spreads out, and the tulip. At noon, on a hot day, you will find the tulip opened nearly flat. At eleven the Star of Bethlehem shuts up, while most of the day flowers are in their best bloom.
At twelve the lazy passion-flowers awake, and the sweet-peas have their banners opened wide. At two the wild daisies are brightest. Then at four in the afternoon, out comes the four-o’clocks, and at five the “beauty of the night,” and at six the delicate evening primrose. At seven the white lychnis, which blooms only at night, opens. Later still the night primrose puts out its white bloom, and at two o’clock in the morning the purple convolvulus wakes up and wonders why the sun is so late.
Now, in sleeping, most of the flowers close tight together. Besides the rest to the growing organs, which sleep brings them, this folding up keeps moisture from the pollen. Also, the flowers, whose partners are day-flying insects, keep out of the way of night insects by closing their pretty doors.
The evening primroses, night lychnis, and others, which have night-flying insect partners, keep shut whenday insects are about. You will notice that most of these night plants have yellow or white petals, and a sweet perfume.
I have told you the leaves sleep also. Leaves sometimes sleep by closing the two halves of the leaf together by the mid-vein. Other leaves sleep by dropping the leaves down against the stem.
A young Swiss girl was one of the first to observe this sleep motion of leaves. She saw it first in the clover. When the leaves sleep in this way, you might think them faded and dying.
You will do well to watch this sleep of leaves. If you go into a garden, or field, or on the road-side, you will see that the leaves look very different after sunset from what they did in the noon-day.
The yellow sorrel and the clover are plants in which you can watch leaf-sleep well. You will find the small leaflets hanging down against the stalk. So if you look at the beans in the garden, you will see their leaves falling back, and perhaps a little bent over. One kind of oxalis, with very small, compound leaves, lifts its leaves up all in a bunch to go to sleep.
The leaves of trees have sleep-change. The mimosa and the barberry close their leaves at night.
Are these sleep motions of any use to plants? Yes.It has been found that this folding up, and falling back of leaves, will help them to resist cold and wet.
If, during a cold night, you pin the leaves out, so they cannot take the sleep position, they are likely to freeze. Also this change in the leaves, at night, helps to shield the plant from too much dew.
Sometimes, also, it is of use as it turns toward the dew the under side of the leaf. This under side has the most mouths for drinking water. Thus the flower has a good drink at night, after the dry, hot day.
Among the other motions of plants, I might speak of that of some leaves, which curl or shrink if you touch them. But I have not space for that now.
Perhaps you think that these lessons have told you a great many things about flowers. If you go on with the study of plants, you will see how much there is to tell, and how very little has here been told.
These lessons are only meant to stir up your interest in plants, and show you what wonders are in the plant world. After that, you will be sure to learn more for yourselves.