EFFECTS OF LIGHT ON ELONGATION AND BRANCHING IN PEA ROOTS

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Abstract
Root elongation and lateral root formation in seedlings and isolated roots of the garden pea, Pisum sativum var. Alaska, grown in a nutrient medium were studied under various conditions of artificial illumination. White light markedly inhibits lateral root formation. The cotyledons act as the source of supply of substances necessary for lateral root formation. Light inactivates the substances within the primary root. Red light inhibits lateral root formation more effectively than filtered blue or green light. Maximum root elongation occurs when roots are maintained in the dark. It is suggested that substances other than auxin are inactivated within the primary root by illumination.