During a 48 hour period after spraying with 2,4–dichlorophenoxyacetic acid (2,4–D), the ribonucleic acid (RNA) in the subcellular particles of soybean hypocotyl tissue doubled with over half of the increase appearing in the microsomal fraction and one quarter in the soluble fraction. It is hoypothesized that the herbicidal action of 2,4–D lies in a renewal of nuclear activity in the tissue, leading to a synthesis of RNA and protein and to tissue proliferation, and that the cytochemical basis of auxin-herbicide action lies in a reversion to a meristematic metabolism.