Rice Seedlings Germinated in Water with Normal and Impeded Environmental Gas Exchange

Abstract

One hundred 'Pyrex' beakers (250-ml with a spout or 400-ml tall-form without a spout) were marked at the 170-cm3 level and were filled to this point with distilled water. The depth of 170 cm3 of water was c. 5*5 cm in either type of beaker, this depth being the same as that employed when broadcasting rice seeds in fields in the United States (Grist 1965). Ten unhulled, unwashed, and unsterilized rice seeds without any fungicidal dressing (Oryza sativa, var. Hokkaido-Carny) were dropped into each of ninety beakers. Only those seeds which sank quickly to the bottom of the beakers when dropped into the water were used. Any seeds that floated after repeated immersion in the water were discarded and replaced with seeds that settled rapidly to the bottom of the beakers. No attempt was made to remove any gas bubbles that became trapped in the hulls of the seeds as long as the seeds settled quickly on the bottom of the vessels. Seeds were not put into the remaining ten beakers. The surface of the water in thirty beakers with seeds and in the ten beakers without seeds was overlayed with 30 cm3 of olive oil per beaker (British Pharmacopoeia Standard). Ten beakers were overlayed with 3 cm3 of olive oil, ten beakers with 1 cm3 of olive oil, and ten beakers with 30 cm3 of liquid paraffin (light grade) per beaker. The surface of the water in the remaining thirty beakers was left with a normal air-water interface (no oil overlay). All beakers of all treatments were covered with thin watch-glasses (7.5 cm diameter) to prevent debris from falling into the vessels and to reduce the evaporation of water from the beakers without an oil overlay. The water level in the beakers without the oil overlay was checked daily and was maintained at the 170-cm3 level by adding distilled water whenever necessary. The 30-cm3 olive-oil overlay was removed from one-half of all treatments containing seeds on the fourteenth day and from the remaining half of these treatments on the twenty-fourth day after the start of the investigation. Oxygen electrode measurements of the water of all treatments were made on the fourteenth and twenty-fourth day just prior to the removal of the 30-cm3 olive oil overlay. The oil layer was removed by filling the