Modern Views on Root Actions of Plants.
By H. O. Askew, Cawthron Institute, Nelson.

Recent views on root action of plants have been away from the previous idea that roots absorbed nutrients from the solution surrounding soil particles. Present ideas on the constitution of the soil postulate clay particles carrying a swarm of ions (H, Ca, Mg, K, etc.) which are “exchangeable.” Root hairs of plants are colloidal systems which may also be surrounded by ionic swarms. Inter-penetration of these swarms of ions may lead to interchange of ions between roots and clay particles. Moreover, movement of nutrients may be both into and out of the roots.

While not at present a complete explanation of the feeding of plants, the “contact exchange” hypothesis forms a good starting point for further work in this branch of plant nutrition.