Developmental studies on Euphorbia esula. Evidence of competition for water as a factor in the mechanism of root bud inhibition

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Abstract
Seedlings of leafy spurge (Euphorbia esula L.) were grown in sand culture under controlled conditions and experiments were designed to test the hypothesis that competition for water between the root buds and the parent shoot is a significant factor in the mechanism of root bud inhibition. It was shown that the water content of the root buds increased by approximately 25% within 24 h of the removal of the parent shoot. Root bud length increased significantly between 24 and 48 h from shoot removal but while some of the buds continued to grow others were apparently reinhibited. Shoots with all immature tissue removed continued to exert a high degree of root bud inhibition but this inhibition was markedly reduced by keeping the plants in a high humidity. Increasing the humidity from approximately 50 to 95% also caused a significant increase in the rate of emergence and elongation of shoots produced from root buds following the removal of the parent shoot. This effect on emergence was suppressed by conditions presumed to reduce the degree of root bud aeration. Taken as a whole, the results lend considerable support to the concept of internal competition for water as a factor in the mechanism of root bud inhibition.