Experiment.—Procure a wide-mouthed bottle, an egg, a glass tube about three inches long and a quarter-inch in diameter, a candle, and a piece of wire a little longer than the tube. Remove a part of the shell from the large end of the egg without breaking the skin beneath. This is easily done by gently tapping the shell with the handle of a pocket-knife until it is full of small cracks, and then, with the blade of the knife, picking off the small pieces. In this way remove the shell from the space about the size of a nickel. Remove the shell from the small end of the egg over a space about as large as the end of the glass tube. Next, from the lower end of the candle cut a piece about one-half inch long. Bore a hole in this just the size of the glass tube. Now soften one end of the piece of candle with the hole in it and stick it on to the small end of the egg so that the hole in the candle comes over the hole in the egg. Heat the wire, and with it solder the piece of candle more firmly to the egg, making a water-tight joint. Place the glass tube in the hole in the piece of candle, pushing it down till it touches the egg. Then, with the heated wire, solder the tube firmly in place. Now run the wire down the tube and break the skin of the egg just under the end of the tube. Fill the bottle with water till it overflows, and set the egg on the bottle, the large end in contact with the water ([Fig. 14]). In an hour or so the contents of the egg will be seen rising in the glass tube. This happens because the water is making its way by osmose into the egg through the skin, which has no openings, so far as can be discovered. If the bottle is kept supplied with water as fast as it is taken up by the egg, almost the entire contents of the egg will be forced out of the tube. In this way water in which plant food is dissolved enters the slender root hairs and rises through the plant.
Experiment.—This process of osmose may also be shown as follows ([Fig. 15]): Remove the shell from the large end of an egg without breaking the skin, break a hole in the small end of the egg and empty out the contents of the egg; rinse the shell with water. Fill a wide-mouthed bottle with water colored with a few drops of red ink. Fill the egg-shell partly full of clear water and set it on the bottle of colored water. Colored water will gradually pass through the membrane of the egg and color the water in the shell. Prepare another egg in the same way, but put colored water in the shell and clear water in the bottle. The colored water in the shell will pass through the skin and color the water in the bottle. Sugar or salt may be used in place of the red ink, and their presence after passing through the membrane may be detected by taste.
CONDITIONS NECESSARY FOR ROOT GROWTH
We have learned some of the things that the roots do for plants and a little about how the work is done. The next thing to find out is:
What conditions are necessary for the root to do its work?
- We know that a part of the work of the root is to penetrate the soil and hold the plant firmly in place. Therefore, it needs a firm soil.
- We know that the part of the root which penetrates the soil is tender and easily injured. Therefore, for rapid growth the root needs a mellow soil.
- We know that part of the work of the root is to take moisture from the soil. Therefore, it needs a moist soil.
- We know that part of the work of the root is to take food from the soil. Therefore, it needs a soil well supplied with plant food.
- We know that roots stop their work in cold weather. Therefore, they need a warm soil.
Another condition needed by roots we will find out by experiment.
Experiment.—Take two wide-mouthed clear glass bottles ([Fig. 16]); fill one nearly full of water from the well or hydrant; fill the other bottle nearly full of water that has been boiled and cooled; place in each bottle a slip or cutting of Wandering Jew (called also inch plant, or tradescantia, and spiderwort), or some other plant that roots readily in water. Then pour on top of the boiled water about a quarter of an inch of oil—lard oil or cotton-seed oil or salad oil. This is to prevent the absorption of air. In a few days roots will appear on the slip in the hydrant water, while only a very few short ones, if any, will appear in the boiled water, and they will soon cease growing. Why is this? To answer this question, try another experiment. Take two bottles, filled as before, one with hydrant water and the other with boiled water; drop into each a slip of glass or a spoon or piece of metal long enough so that one end will rest on the bottom and the other against the side of the bottle, and let stand for an hour or so ([Fig. 17]). At the end of that time bubbles of air will be seen collecting on the glass or spoon in the hydrant water, but none in the boiled water. This shows us that water contains more or less air, and that boiling the water drives this air out. The cutting in the boiled water did not produce roots because there was no air in it and the oil kept it from absorbing any.
Experiment.—Into some tumblers of moist sand put cuttings of several kinds of plants that root readily ([Fig. 18]), geranium, tradescantia, begonia, etc. Put cuttings of same plants into tumblers filled with clay that has been wet and stirred very thoroughly, until it is about the consistency of cake batter. Keep the sand and puddled clay moist; do not allow the clay to crack, which it will do if it dries. The cuttings in the sand will strike root and grow, while most, if not all, those in the clay will soon die. The reason for this is that the sand is well ventilated and there is sufficient air for root development, while the clay is very poorly ventilated, and there is not sufficient air for root growth.
These experiments show us that to develop and do their work roots need air or a well-ventilated soil.