Density of Root Branching as affected by Substrate and separate Ions

An experimental technique has been devised to investigate the possibility that the colloidal substances in the soil, such as humus and clay, might have some specific influence on density of branching of roots. Results were indeed obtained which demonstrate that in model experiments peat and clay stimulate the outgrowth of many laterals. By using resinous ion exchangers it has been possible to investigate the effect of a single ion on root branching. Complementary experiments, in which the influence of nutrient solutions deficient in one element, were tested, were also performed. The techniques used have been described. It could be demonstrated that the sequence of activity is NOT > H2POT, K+ > Ca++, Mg++ > SO4 . These results were obtained with peas. N-deficient solutions have the opposite result as NOa alone. Indications were obtained that a deficiency in P may result in effects comparable to those of high N. The effect of peat and clay in these experiments is ascribed to the high ionic concentrations of the adsorbed ions. This explanation of our results seems justified by comparing the effects of an anion exchange resin with that of a cation exchange resin. A discussion of the results is given.