THE GLASS POND
Have you ever had an indoor pond? Such a pond is easy to make and one can watch the life of the water in it even better than outdoors, where the ponds are too large and have too much in them. Besides, when out-of-doors, one is likely to be disturbed by passers-by.
For my indoor pond, the blacksmith made me a framework of iron rods. The carpenter, who is also a glazier, set the framework on a wooden base and supplied it with a movable board as a lid; he then fixed thick panes of glass in the four sides. The bottom of the pond was made of tarred sheet iron, and had a trap to let the water out. The contrivance looked very well, standing on a little table in front of a sunny window. It held about ten or twelve gallons.
I put in it first some limy incrustations with which certain springs in my neighborhood cover the dead clumps of rushes. It is light, full of holes, and looks a little like a coral reef. Moreover, it is covered with a short, green, velvety moss of tiny pond-weed. I count upon this pond-weed to keep the water healthy. How? Let us see.
The living creatures in the pond fill the water, just as living people fill the air, with gases unfit to breathe. Somehow the pond must get rid of these gases, or its inhabitants will die. This is what the pond-weed does; it breathes in and burns up the unwholesome gases, changing them into a life-giving gas.
If you will look at the pond when the sun is shining on it, you will see this change take place. How beautiful the water-weeds are! The green-carpeted reef is lit up with countless sparkling points and looks like a fairy lawn of velvet, studded with thousands of diamond pin-heads. From this exquisite jewelry pearls constantly break loose and are at once replaced by others; slowly they rise, like tiny globes of light. They spread on every side. It is a constant display of fireworks in the depth of the water.
This is what is really happening: The weeds are decomposing—that is, separating into its elements—the unwholesome carbonic acid gas with which the water is filled; they keep the carbon to use in their own cells; they breathe out the oxygen in tiny bubbles, the pearls that you have seen. These partly dissolve in the water, making it healthful for the little water-creatures to breathe, and partly reach the surface, where they vanish in the air, making it good for us to breathe.
No matter how often I see it, I cannot help being interested in this everyday marvel of a bundle of weeds purifying a stagnant pool; I look with a delighted eye upon the ceaseless spray of spreading bubbles; I see in imagination the prehistoric times when seaweed, the first-born of plants, produced the first atmosphere for living things to breathe at the time when the land of the continents was beginning to rise out of the oceans. What I see before my eyes, between the glass panes of my pond, tells me the story of the planet surrounding itself with pure air.
CHAPTER II
THE CADDIS-WORM
[The caddis-worm is the grub of the caddis-fly, which is like a small moth and is often seen flitting over our streams and ponds. There are about one hundred and fifty species of this fly in America.]
Whom shall I lodge in my glass trough, kept always wholesome by the action of the water-weeds? I shall keep Caddis-worms, those insects which clothe themselves with little sticks and other materials. They are among the most ingenious of the self-clothing insects.
The particular species of Caddis-worm I have chosen is found in muddy-bottomed, stagnant pools crammed with small reeds. It is the little grub that carries through the still waters a bundle of tiny fragments fallen from the reeds. Its sheath, a traveling house, is an elaborate piece of work, made of many different materials.
The young worms, the beginners, start with a sort of deep basket in wicker-work, made of small, stiff roots, long steeped and peeled under water. The grub that has made a find of these fibers saws them with its jaws and cuts them into little straight sticks, which it fixes one by one to the edge of its basket, always crosswise. This pile of spikes is a fine protection, but hard to steer through the tangle of water-plants. Sooner or later the worm forsakes it, and builds with round bits of wood, browned by the water, often as wide as a thick straw and a finger’s breadth long, more or less—taking them as chance supplies them.
It does not always use wood, however. If there are plenty of small, dead Pond-snails in the pond, all of the same size, the Caddis-worm makes a splendid patchwork scabbard; with a cluster of slender roots, reduced by rotting to their stiff, straight, woody axis, it manufactures pretty specimens of wicker-work like baskets. With grains of rice, which I gave the grubs in my glass pond as an experiment, they built themselves magnificent towers of ivory. Next to the sheaths of snail-shells, this was the prettiest thing I ever saw the Caddis-worms make.