Effect of Low Temperatures on Germination of Impermeable Seeds

Abstract

1. Dormancy of seeds due to an impermeable seed coat may often be broken by cooling the seeds to very low temperatures. 2. Impermeable sweet clover and alfalfa seeds may be made permeable without injuring, by freezing the air-dry seeds in liquid air (-190⚬C.). 3. Sweet clover seeds were not injured by keeping them in liquid air for nearly six months (175 days); and rapidly cooling seeds down to -190⚬C. twenty times, followed each time by a very rapid warming, did not injure them. 4. Cooling to -80⚬C. caused most of the impermeable alfalfa seeds to become permeable, but this treatment had very little effect on impermeable sweet clover seeds. 5. Freezing air-dry seeds to very low temperatures had no appreciable effect on their keeping power. 6. The average specific heat of air-dry alfalfa seeds between 20⚬ and -190⚬C. is about 0.21 cal. per degree. 7. The process of destroying the impermeability of alfalfa seeds by intense freezing appears to be a practical one for large-scale operations.