Plants and their ways in South Africa . hat becomes of thewater ? Place the upper part of theplant cut off in the last experiment ina slender jar of water. Pour a layerof oil over the top to prevent evapora-tion, or thrust the cut end through astopper and seal with wax. Coverthe whole with a bell-jar or a that the glass is quite dry beforecovering. In a short time the jar willbe lined with a thin mist, which willcollect in drops of water. Water passes from thePlant in the form of Vapour. As the leavesvapour more water is drawn up to take its place. Ex. 22. Soak strips of paper in
Plants and their ways in South Africa . hat becomes of thewater ? Place the upper part of theplant cut off in the last experiment ina slender jar of water. Pour a layerof oil over the top to prevent evapora-tion, or thrust the cut end through astopper and seal with wax. Coverthe whole with a bell-jar or a that the glass is quite dry beforecovering. In a short time the jar willbe lined with a thin mist, which willcollect in drops of water. Water passes from thePlant in the form of Vapour. As the leavesvapour more water is drawn up to take its place. Ex. 22. Soak strips of paper in cobalt chloride. Dry thoroughly, andnotice how they change from red to blue as they dry. Dry the inside ofthe jar containing the plant. After remaining in the bell-jar lor a whilethe paper changes back to red. This also shows that vapour is passingfrom the leaves. 1 This pressure accounts only in part for the upward ascent, whichis not fully understood. Evaporation from the leaf surface is doubtlessconnected with the lifting of -M Fig. 67.—Apparatus to demon-strate root-pressure. The cutstem is fastened to a glass tubeby means of rubber tubing. Thetube leads by an arm into thejar (J). Both are filled with waterwith mercury in the bottom ofthe jar. As the cells in the rootforce the water into the tube themercury is forced up into thesmall tube, t. Leaves and Stem of a give off 6o Plants and their Ways in South Africa This pretty experiment should not be omitted. Cobalt chloride maybe obtained from the chemist. Sixpennyworth will prepare sufficientpaper to last some time. It will keep, and the same piece may be usedrepeatedly. Ex. 23. Place under the bell-jar fruits of Eroditim or Pelargonium andwatch them uncoil; remove, dry in the sun, and repeat the experiment. Ex. 24. Place a leafy shoot in a glass U-tube (a straight piece ofglass may be heated and bent the required shape). Connect the shoot tothe tube with rubber tubing so that no air can enter. The tube should be
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Keywords: ., bookcentury1900, bookdecade1910, booksubjectplants, bookyear1915
