Fig. 1.

Experimental system for the study of hydrotropism-influenced root system development in soil. (A) Fourteen-day-old plants were placed in the bottom of a transparent rectangular dish (14 × 10 × 1·5 cm). (B, C) The seedling roots were covered with soil (1·5 cm depth and 11 cm length). To maintain uniformly higher water content (Control), a block of water-absorbent plastic foam (1 × 1 × 11 cm; indicated by hatched bars) containing 10 mL distilled water was placed on each side of the soil, and the dish was entirely covered with a lid (B). To establish moisture gradients (Hydrostimulated), the water-absorbent plastic foam containing 10 mL distilled water was placed only on one side of the soil, and the half of the container with the plastic foam was covered with a lid (C). To maintain the moisture gradient in the hydrostimulated chamber for a longer time, 10 mL water was supplied to the plastic foam through the injection port every 5 d during the experiment. The chambers were held at an angle of 5 ° from the vertical to promote root growth along the transparent bottom side of the dish. Plants were grown under these conditions for 30 d.