. Contributions from the Botanical Laboratory and the Morris Arboretum of the University of Pennsylvania, vol. 14. Botany; Botany. 456 PLANT PHYSIOLOGY Changes in ionic concentration of the solutions surrounding the roots were followed by means of daily measurements of electrical resistance, from which were derived the corresponding specific conductance values, computed for a temperature of 18° C. Daily measurements of hydrogen-ion concen- tration were made by means of the quinhydrone-titration method, with McIlvaine^s buffers (4). Since the temperature coefficient of hydrogen- ion concentrat
. Contributions from the Botanical Laboratory and the Morris Arboretum of the University of Pennsylvania, vol. 14. Botany; Botany. 456 PLANT PHYSIOLOGY Changes in ionic concentration of the solutions surrounding the roots were followed by means of daily measurements of electrical resistance, from which were derived the corresponding specific conductance values, computed for a temperature of 18° C. Daily measurements of hydrogen-ion concen- tration were made by means of the quinhydrone-titration method, with McIlvaine^s buffers (4). Since the temperature coefficient of hydrogen- ion concentration is so small as to be negligible in such a study as this (7), the pH values were not corrected for temperature. Daily observations con- cerning the appearance of the plants w^ere also made, particularly with regard to development and visible injury. In the following subsections, changes in the media will be presented first, distilled water and the several acid solutions being considered in order, and then attenion will be turned to records of growth and of injury to the plants. Experimentation Changes in the media Distilled w^ater.âFigure 1 presents graphically average daily con- CONDUCTANCE o o o o H,0 1 1 / ^7 if f l\ c \/ ru r LAN T5. 1 J2«> ^ k J y^ ^ WITHOUT P " " T T " "~ - I234 56789DIII2I3 DAYS Fig. 1. Conductance (millionths recip. ohm) of HjO with and without seedlings. Circles mark end of rapid initial increase in pH; arrows mark onset of visible root injury. ductance values for HoO with and without seedlings at 22° C., and for HoO with seedlings at 28° C. Since no considerable conductance increase oc- curred without plants, it may be inferred that the increases shown by water with plants were due to outward movement of material from the roots. There was continuous exosmosis of electrolytes, in excess of any absorption that may have occurred. Net exosmosis, which was at first relatively slow, became markedly accelerated about the
Size: 910px × 2747px
Photo credit: © The Book Worm / Alamy / Afripics
License: Licensed
Model Released: No
Keywords: ., bookcentury1900, bookpublisherphiladelphiasn, booksubjectbotany
