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 lot 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). =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._ =94.= Cut a succulent shoot of any plant, thrust the end of it through a hole in a cork, and stand it in a small bottle of water. Invert over this a fruit jar, and observe that a mist soon accumulates on the inside of the glass. In time drops of water form. =95.= The experiment may be varied as shown in Fig. 125. =96.= Or, invert the fruit jar over an entire plant, as shown in Fig. 126, taking care to cover the soil with oiled paper or rubber cloth to prevent evaporation from the soil. =97.= The test may also be made by placing the pot, properly protected, on balances, and the loss of weight will be noticed (Fig. 127). =98.= Cut a winter twig, seal the severed end with wax, and allow the twig to lie several days; it shrivels. There must be some upward movement of water even in winter, else plants would shrivel and die. =99.= _To illustrate sap pressure._ The upward movement of sap water often takes place under considerable force. The cause of this force, known as _root pressure_, is not well understood. The pressure varies with different plants and under different conditions. To illustrate: cut off a strong-growing small plant near the ground. By means of a bit of rubber tube attach a glass tube with a bore of approximately the diameter of the stem.