Fig. 122.—To show the Escape of Oxygen.
89. Make the experiment illustrated in Fig. [122]. Under a funnel in a deep glass jar containing fresh spring or stream water place fresh pieces of the common waterweed elodea (or anacharis). Have the funnel considerably smaller than the vessel, and support the funnel well up from the bottom so that the plant can more readily get all the carbon dioxide available in the water. Why would boiled water be undesirable in this experiment? For a home-made glass funnel, crack the bottom off a narrow-necked bottle by pressing a red-hot poker or iron rod against it and leading the crack around the bottle. Invert a test-tube over the stem of the funnel. In sunlight bubbles of oxygen will arise and collect in the test-tube. If a sufficient quantity of oxygen has collected, a lighted taper inserted in the tube will glow with a brighter flame, showing the presence of oxygen in greater quantity than in the air. Shade the vessel. Are bubbles given off? For many reasons it is impracticable to continue this experiment longer than a few hours. 90. A simpler experiment may be made if one of the waterweeds Cabomba (water-lily family) is available. Tie a number of branches together so that the basal ends shall make a small bundle. Place these in a large vessel of spring water, and insert a test-tube of water as before over the bundle. The bubbles will arise from the cut surfaces. Observe the bubbles on pond scum and waterweeds on a bright day. To illustrate the results of respiration (CO2).
Fig. 123.—To illustrate a Product of Respiration.
Fig. 124.—Respiration of Thick Roots.
91. In a jar of germinating seeds (Fig. [123]) place carefully a small dish of limewater and cover tightly. Put a similar dish in another jar of about the same air space. After a few hours compare the cloudiness or precipitate in the two vessels of limewater. 92. Or, place a growing plant in a deep covered jar away from the light, and after a few hours insert a lighted candle or splinter. 93. Or, perform a similar experiment with fresh roots of beets or turnips (Fig. [124]) from which the leaves are mostly removed. In this case, the jar need not be kept dark; why? To test transpiration.
Fig. 125.—To illustrate Transpiration.