The experimental material consisted of root segments excised from grape cuttings maintained in nutrient culture. In every experiment reported here washed roots absorbed Rb at substantially higher rates than unwashed root segments. The absorption of Rb per unit weight of root was generally in the same low range for unwashed roots with little regard to diameter, age, browning, or the presence of an intact root apex. On the other hand, after washing, uptake was much higher in large diameter roots than smaller ones, higher in white roots than in brown ones, and higher in younger tissues than older ones, The response to washing is markedly reduced by the presence of an intact attached root apex.INTRODUCTION This paper represents the first report of a more extensive study underway focused on both the absorption and translocation of potassium in grape roots using rubidium as a chemical analog of potassium. Here we examine the responses of grape roots to two kinds of variables: First, mineral absorption in relation to the morphological variables in grape roots: (a) root diameter; (b) brown versus white roots; (c) absorption in different regions of the root. Second, the mineral absorption as influenced by experimental variables: (a) the washing response; (b) the presence of the intact root apex and the time of its excision; (c) temperature of certain steps in the procedures. NORTON AND SMITHMost of the work which has been done on the mechanisms of mineral absorption by plants has utilized roots of herbaceous plants, and practically all of the work which has been published on the washing response has utilized roots of grasses. Although the washing response has received only occasional attention (4,5,11,12,13), it is a remarkable manifestation of the influence which the root apex exercises over ion absorption by older cells of the root, and its eventual clarification will contribute to understanding of the complex physiological interrelationships within the root. This response is distinctly different from that described by Van Steveninck (16), to which the term "aging" might properly be applied since aging occurs over a period of many hours and involves growth and production of new cells. The experiments presented here represent, so far as we are aware, the first published examination of the washing response in a woody, perennial dicot. On the more general subject of ion absorption by grape roots, significant research completed in the past few years includes: a study on the absorption of water and mineral ions through suberized and unsuberized grape roots (13); a very thorough analysis of the organic and inorganic solutes present in xylem fluid of grape (1, 2); and pioneering work on kinetics of ion absorption by grape roots, by Magionni (7,8,9,10,17). The latter work, however, did not investigate the washing response. The data presented here from our experiments show that the washing responses of the grape roots are similar in many respects to responses shown by corn, but there are some significant differences. MATERIALS A...