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the tendency of the growing organs of plants, particularly the roots, to grow away from a less moist environment toward a moister one. Where there is an uneven distribution of moisture in the soil, plant roots are directed to the moister areas because of hydrotropism. Hydrotropic sensitivity is concentrated in the very tip of the root. Sometimes negative hydrotropism is observed. For example the sporangiophores of many molds grow away from a moist substratum.