. Essentials of biology presented in problems. Biology. LEAVES AND THEIR WORK 127 distributed to the air during twenty-four hours by a grass plot twenty-five by one hundred feet, the size of the average city lot. According to Ward, an oak tree may pass off two hundred and twenty-six times its own weight in water during the season from June to October. From which Surface of the Leaf is Water Lost? — In order to find out whether water is passed out from any particular part of the leaf, we may re- move two leaves of the same size and weight from some large-leaved plant — a mullein was used for th
. Essentials of biology presented in problems. Biology. LEAVES AND THEIR WORK 127 distributed to the air during twenty-four hours by a grass plot twenty-five by one hundred feet, the size of the average city lot. According to Ward, an oak tree may pass off two hundred and twenty-six times its own weight in water during the season from June to October. From which Surface of the Leaf is Water Lost? — In order to find out whether water is passed out from any particular part of the leaf, we may re- move two leaves of the same size and weight from some large-leaved plant — a mullein was used for the illustrations given below — and cover the. Experiment to show through which surface of a leaf water passes off. upper surface of one leaf and the lower surface of the other with vaseline. The petioles of each should be covered with wax or vaseline, and the two leaves exactly balanced on the pans of a balance which has previously been placed in a warm and sunny place. Within an hour the leaf which has the upper surface covered with vaseline will show a loss of weight. Examination of the surface of a mullein leaf shows us that the lower sur- face of the leaf is provided with stomata. It is through these organs, then, that water is passed out from the tissues of the leaf. Regulation of Transpiration. — The stomata of leaves close at night. On days when there is little humidity, they also tend to close, retarding transpiration, but when the water supply is abundant they open, increas- ing transpiration. This automatic action is of very great importance to the life of a plant, since evaporation of water is thus regulated. The Effect of Transpiration on Water within the Stem. — It has al- ready been noted that root pressure alone will not account for the rise. 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 w
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Keywords: ., bookcentury1900, bookdecade1910, booksubjectbiology, bookyear1911
