HOW DOES EROSION AFFECT SOILS? (XXV-1)

The problem. Fertile soils contain much finely divided materials and much organic matter. These things are more readily washed away than are coarser soil substances. What are the effects of running water upon soils?

What to use. An open ditch, banks of a stream or lake, a city curb during or immediately following a heavy rain, an improvised stream over some soil in a well-drained sink.

What to do. 1. This study is best carried out by a visit to a running stream, a lake shore, or a hillside where ravines have been formed (Fig. 148 of the text). An open drainage ditch will usually furnish a good basis for this work. Observe the running water to determine whether it is carrying any soil particles. 2. Photographs should be made of all important examples of erosion.

Questions. Does rapidly running water carry more material or larger pieces than slowly running water? Where does the material come from? What becomes of this material? How does the carrying power of water change with changes in its rate of flow? What evidences upon this question are found along banks and riffles of lakes, streams, and ditches?

Suggestions for report. Make diagrams or photographs of one or more illustrations of erosion and describe what has occurred. Suggest a means for preventing erosion.

Reference work. Read sections 308 to 313, also bulletins or correspondence from your state agricultural college upon erosion in relation to soils.

Optional problems. Arrange an erosion model in a sink in the following manner. Fill one end of the sink with sandy or gravelly soil; close the outlet of the sink by use of a stopper

through which a short glass tube is inserted so that an inch or two of water will stand in that end of the sink before the water overflows; by use of a tube allow a small stream of water to run very slowly upon the soil farthest from the outlet. Observe the development of channels and the deposit of materials. If in an open field erosion is allowed to continue unhindered, what results will follow? Is it the better or poorer parts of the soil which are usually lost by erosion? Fill a glass jar or bottle with muddy water from a rapidly flowing stream and after a day or two see any solid materials have settled from the water.

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HOW PLANT ROOTS ABSORB WATER (XXVII-1)

The problem. It is commonly said that plants cannot live without moisture. Water enters plants almost wholly through the roots. Can we demonstrate the entrance of water into plants?

What to use. Carrot (or beet) at least two inches in diameter and five or six inches long, one-hole rubber stopper, glass tube five feet long, apple corer, corn sirup, plastic clay, rubber bands, and quart jar.

What to do. 1. Bore a hole two inches deep in the top of the carrot (or beet) to fit the stopper. An apple corer is convenient for this work. Fill the hole half full with sirup. Add water, then stop the hole with the rubber stopper in which the glass tube has been inserted. Press some plastic

FIG. 44

clay around the stopper.

Fasten the whole apparatus in an upright position (Fig. 44), the carrot being submerged in a jar of water almost to the stopper.

2. Observe and record hourly the rise of liquid in the tube.

Questions. Why was sirup placed in the hole in the carrot? If no sirup is placed in the hole and the carrot (or beet) is placed in a thick sirup instead of water, what results will follow?

Suggestions for report. Diagram the apparatus used and write a report in which you tell what was done, what happened, and how this experiment illustrates the action of plant roots.

Reference work. Read sections 319 to 325.

Optional problems. Cut off the top of a potted woody or semiwoody plant, cutting it about three inches from the soil. To the stump of the plant attach a small-bore glass tube in a vertical position. It is sometimes necessary to insure a tight joint by wrapping the rubber tubing with cord or wire. Water the soil freely and observe daily to see if water rises in the glass tube. Try the demonstration diagrammed in figure 156 of the text. Why is it that a grapevine when cut in the springtime "bleeds"? Do other plants act in the same way? When maple trees are "tapped," what is the source of the water which comes from the wound?