Some Neglected Soil Factors in Plant Growth 1

The difl~culty of growing normal plants in synthetic media is one of common experience. The reason is self-evident, for all the factors that influence plant growth are not well understood. In the matter of nutrition alone there is increasing evidence that more than ~ o of the So-odd chemical elements known are essential and indispensable to the life and growth of green plants. Some elements have ap-. parently been overlooked owing to the fact that they are required in such small amounts, that either they have been supplied accidentally as impurities in the nutrient salts, or else the growth of the plant was continued for such a short period that the needs were supplied by small amounts stored in the seed. Aside from the additional elements which may be essential for plant growth, there are factors connected with possible toxic conditions which may be important. Certain kinds of finely divided or colloidal material, such as kaolin, silica, and ferric oxide, which are found in soils may, when added to culture media, combine chemically or physically with toxic material produced in the culture media or excreted by plant roots, thus inhibiting the action of the toxins and greatly favoring root development and pl’ant growth. That there may be factors of this kind is indicated by observations to the effect that plants usually grow better in a good soil than in the best artificial medium, that may be prepared. It was the purpose of this investigation to study some of the more or less neglected soil factors in plant growth which have just been mentioned. REVIEW OF LITERATURE