. The chemistry and mode of action of plant growth substances; proceedings of a symposium held at Wye College, University of London, July 1955. Plant regulators; Auxin; Growth (Plants). Tirs Figure 1. Per cent extensions of oat coleoptiles plotted against time in hours: without lAA, with lAA 1 mgjl. and lAA 10 mgjl. The figures at the right-hand side of each curve show the osmotic pressures of potassium chloride solutions in which the extension growth took place. but one inclines to the view that the increase at low auxin concentrations is possibly due to increased wall plasticity and the redu
. The chemistry and mode of action of plant growth substances; proceedings of a symposium held at Wye College, University of London, July 1955. Plant regulators; Auxin; Growth (Plants). Tirs Figure 1. Per cent extensions of oat coleoptiles plotted against time in hours: without lAA, with lAA 1 mgjl. and lAA 10 mgjl. The figures at the right-hand side of each curve show the osmotic pressures of potassium chloride solutions in which the extension growth took place. but one inclines to the view that the increase at low auxin concentrations is possibly due to increased wall plasticity and the reduction at higher concentra- tions may be explained on the basis of reduced activity of pumping mechanisms. As it has been suggested that lAA increases water secretion, it may be well to record here that Dr. J. F. Sutcliffe (private communication) has shown that lAA, while having little effect on ion secretion at low concentrations, definitely inhibits ion uptake by actively absorbing beet tissue at higher concentrations such as 10""* M and over. The same set of data can be used to obtain estimates of the osmotic pressure of tissue by noting the external above which further shrinkage does not occur. Unfortunately, although one tends to expect that a plas- molysed tissue will not shrink on being placed in a hypertonic solution, considerable shrinkage does occur when plasmolysed cells are more strongly plasmolysed, especially in young extending tissues, though the increments of shrinkage are much less. One cannot therefore get an accurate estimate, but the data suggest values of around 18 atm at the lower auxin concentra- tions and 13 atm in the case where the concentration was 10 mg/1. The difference (—) gives an estimate of the wall pressure. The 285 19a. 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 th
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