The development of the root system inAllium cepawas followed for periods of up to 25 days after emergence of the radicle from the seed. Apical meristem activity, in terms of mitotic index, the percentage of cells undergoing DNA synthesis, and cell doubling time, was maximal within several days of emergence in both the primary and adventitious roots, but it gradually decreased in the subsequent period of growth. These changes in proliferative activity in individual roots were paralleled by concurrent changes in elongation rate. Thus, the period of maximum cell production, as well as that of elongation, was of limited duration in each root. Throughout the period of study, the most recently emerged root displayed the highest level of proliferative activity, relative to that found in the other roots on the plant. Changes in the rate of growth of individual roots appeared to be correlated with the early growth of the succeeding root.Key words:Allium, onion, root development, meristem, primordium.
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