. Contributions from the Botanical Laboratory, vol. 7. Botany; Botany. I ^ 386 AMERICAN JOURNAL OF BOTANY [Vol. 17, May, 19301 RESPIRATION 387 it does not seem necessary to exhaust the enclosed air of CO2 each time, as the principle of increasing and reducing the CO2 concentration is involved. Time is wasted by carrying exhaustion far beyond the upper standard, for time will be needed for the return of the CO2 concentration. Therefore, the time was calculated so that it required from one half to one minute to reach the upper standard after the current was switched from the NaOH tube. Se
. Contributions from the Botanical Laboratory, vol. 7. Botany; Botany. I ^ 386 AMERICAN JOURNAL OF BOTANY [Vol. 17, May, 19301 RESPIRATION 387 it does not seem necessary to exhaust the enclosed air of CO2 each time, as the principle of increasing and reducing the CO2 concentration is involved. Time is wasted by carrying exhaustion far beyond the upper standard, for time will be needed for the return of the CO2 concentration. Therefore, the time was calculated so that it required from one half to one minute to reach the upper standard after the current was switched from the NaOH tube. Several readings were recorded until at least three were constant. They were taken as the normal rate of respiration. The plants thus calibrated were then changed from tap water to a salt solution, in which the stems were cut just above the ground line. By this means the solution enters the plant directly. After returning the plants into the chamber, the preceding operation was repeated. At regular intervals readings were recorded, giving points from which a curve representing the effect of the given solution could be drawn. The chlorids of Cu, Cd, Al, Fe, Mg, and Na were used in these experi- ments. Various concentrations of each salt were tried in order to discover the ranges of molar concentration that cause a stimulation of the production of CO2. The range is practically of the same width for each metal but does not occur at the same molar concentrations for the different salts tried. The reciprocal of the time required to change the color from pH to was taken as the rate of respiration or CO2 production. After reaching the lower end point, the CO2 was removed by passing the air through the NaOH after which the indicator returned to its original color. The time required to change it was again noted. By this means a series of readings was taken from which a curve was made by plotting time against the output of CO2. In general, they are of the same nature, but differ
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