Quantitative Studies of Root Development II. Growth in the Early Stages of Development

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Abstract
The growth of the root systems of barley seedlings was measured at dally intervals for the first 2 wk. after germination. The lengths and numbers of primary and higher-order branches were recorded and relative rates of extension and multiplication together with mean extension rates were derived from the data. An earlier suggestion that root growth rates are high early in plant development but then fall to a lower level was supported by the data which also demonstrated changes in growth rate associated with the initiation of secondary and tertiary roots. A high nutrient concentration reduced root growth both by a transient effect on germination rate and a continuing reduction in mean extension rate. Nutrient effects on branch root production were traceable to these effects on elongation of the parent root.