. Elementary botany. Botany. TRANSPIRA TTON. 45 S7. Lifting power of transpiration, -Not only clofs transpiration go on quite intiojjenrlunth" of root pressure, as we ha\e rlisco\'ered from other experiments, bat transpiration is eapable of exerting a lifting ]jo\ver on the water in the plant. This may be demonstrated in the following wav: Place the cut end of a leafy shoot in one end of a U tube and lit it water-tight. Partly fill this arm of the U tube with water, and add mercur^• to the other arm until it stands at a level in the two arms as in fig. 54. In a short time we note that the
. Elementary botany. Botany. TRANSPIRA TTON. 45 S7. Lifting power of transpiration, -Not only clofs transpiration go on quite intiojjenrlunth" of root pressure, as we ha\e rlisco\'ered from other experiments, bat transpiration is eapable of exerting a lifting ]jo\ver on the water in the plant. This may be demonstrated in the following wav: Place the cut end of a leafy shoot in one end of a U tube and lit it water-tight. Partly fill this arm of the U tube with water, and add mercur^• to the other arm until it stands at a level in the two arms as in fig. 54. In a short time we note that the mercury is rising in the tube. 88. Hoot pressure may exceed transpiration.—If we cover small activeh' growing plants, such as the pea, corn, wheat, bean, etc., with a bell jar, and place them in the sunlight where the temperature is suitable for growth, in a few hours, if conditions are fa\'orable, we shall see that there are drops of water standing out on the margins of the leaves. These drops of water have exuded through the ordinary stomata, or in other cases what are called water stomata, through the inlluence of root pressure. The plant being covered by the glass jar, the air soon becomes saturated with moisture and transpiration is checked. Root pressure still goes on, howe\'er, and the result is shown in the exuding drops. Root pressure is here in excess of transpiration. This phenomenon is often to be observed during the sum- mer season in the case of low-gro«-ing plants. During the bright warm day transpiration —"^ equals, or may be in excess of, pjg ,,^ root pressure, and the leaves Estimation of the amount of are consequently tlaccid. .\s. Fig. 54. Experiment to show lifting power of Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of these illustrations may not perfectly resemble the original Atkinson, George Francis, 1854-1918. N
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