. Elementary botany. Botany. 34 PHYSIOLOG V. plants in the open niav be used if it is |")referi"c'l, Init plants e seen to higher and higher tip in the tube when obser\'ed at C|uite short intervals. (To meastire the force of rof)t pressure is rather difhcult for elementary' work. To measure it see Ganong, Plant Physiology, pp. 67, 68, or some other book for advancefl 67. In either case where the experiment is continued for several da}'s it is noticed tliat the column of water or of mercury rises and falls at different times during the same dav, tliat is, the column st
. Elementary botany. Botany. 34 PHYSIOLOG V. plants in the open niav be used if it is |")referi"c'l, Init plants e seen to higher and higher tip in the tube when obser\'ed at C|uite short intervals. (To meastire the force of rof)t pressure is rather difhcult for elementary' work. To measure it see Ganong, Plant Physiology, pp. 67, 68, or some other book for advancefl 67. In either case where the experiment is continued for several da}'s it is noticed tliat the column of water or of mercury rises and falls at different times during the same dav, tliat is, the column stands at varvinn; heights; or in other words the root presssure varies during the dav. With some plants it has been found that the pressure is greatest at certain times of the day, or at certain seasons of the year. Such variation of root pressure exhibits what is termed a periodicity, and in the case of some plants there is a daily periodicity; while in others there is in addition an annual periodicity. With the grape vine the root pressure is greatest in tire forenoon, and decreases from 12-6 , while with the sunflower it is greatest l)eforc 10 , when it begins to decrease. Temperature of the soil is one of the most important external conditions affect- ing tlie activity of root Fi?. 45- Experiment tf) show ruot pressure (Detmer).. 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. New York : H. Holt
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