1. The specimen of polygalacturonic acid used in these studies was shown to contain very little neutral sugar, methyl ester groups or ash, and only residues of galacturonic acid. Its electrophoretic homogeneity was examined in pyridine–acetic acid buffer at pH6·5 and in borate buffer at pH9·2. The distribution of effective particle weights was shown to be fairly narrow. 2. The pH-titration curve of the polymer gave a p K value of 3·7. 3. The interaction of the polymer with Ruthenium Red was studied and titration curves were obtained for the spectral shifts associated with the formation of a complex. 4. Optical-rotatory-dispersion studies showed that the Drude constant, λ c , was dependent on pH. 5. Polygalacturonic acid was shown to display non-Newtonian properties in solution and to have an anomalously high relative specific viscosity at low concentrations. 6. Studies were made of the pH-dependence of the sedimentation coefficient of the polymer. 7. These results are discussed in terms of the structure of the molecule and their relevance to the properties of pectic substances.

A method is described for the detection and estimation of radioactive polysaccharides separated by zone electrophoresis on glass-fibre paper.

1. d -Glucose and l -arabinose serve as precursors of the pectic polysaccharides of sycamore suspension-callus tissue. 2. The rates and characteristics of the incorporation of radioactive sucrose, glucose and meso inositol by sycamore callus tissue have been compared and shown to be different. 3. The time-course of the incorporation of radioactive glucose into the major fractions within the cells has been determined. Approx. 7–10% of the radioactivity incorporated is present in the whole pectin of the cells. 4. A study of the continuous incorporation of radioactive glucose showed that the neutral arabinan–galactan fraction of the pectin quickly became saturated with the radioactive label. During the incorporation of radioactivity from a pulse of radioactive glucose the neutral fraction became progressively less labelled, with a corresponding increase in the radioactivity of the weakly acidic pectinic acid, which is known to contain neutral sugars. 5. When the cells were exposed to a pulse of radioactive l -arabinose, the label accumulated first in the neutral fraction and then after 4hr. it passed to the weakly acidic pectinic acid with a corresponding decrease in the radioactivity of the neutral fraction. 6. The product that was initially labelled during the first hour of exposure of the cells in the stationary phase to radioactive glucose was identified as an incompletely methylated galacturonan in which the radioactivity was present in the anhydrogalacturonide residues. This polysaccharide probably acts as the precursor of the polyuronide portions of both the strongly acidic and weakly acidic pectinic acids. 7. The observations are discussed in relation to the structure of the pectic substances and their function in cell growth and development. A tentative model for their metabolic relationship is put forward.