หน้า 85
the roots always grow downwards, in the direction of gravity. the roots show positive geotropism. this enables the roots to penetrate deep in to the soil to find water and anchor firmly in to the soil for support.
the shoots grow upwards, away from gravity. the shoots are said to show negative geotropism. this ensures that the shoots receive enough sunlight for photosynthesis.
hydrotropism is the growth movement shown by plants in response to water.
roots are said to be positively hydrotropic. they grow towards water.
inf face, the response of the roots to water is stringer than their response to gravity. they can grow sideways or upwards in the dirction of a water source, ignoring the gravity pull.
minerals dissolve in water. therefore, the positive hydrotropism shown by the roots helps plants to get enough water and minerals to maintain normal growth