Effects of low temperatures on the loss of innate dormancy and the development of induced dormancy in seeds of Rumex obtusifolius L. and Rumex crispus L.

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Abstract
It is possible to remove the innate dormancy of seeds of Rumex crispus L and Rumex obtusifolius L. by an initial period of low‐temperature stratification, providing the seeds are then transferred to a higher temperature. The lower the initial temperature within the range 1.5°‐15°C, the greater the germination; there is no stratification effect at 20°C. Although 10°C and 15°C were shown to be suitable for both stratification and for the process of germination itself, neither temperature results in any germination if given constantly: a change from a lower to a higher temperature is essential.The optimum period for stratification depends on two separate processes which occur during the treatment–a rapid loss of innate or primary dormancy and a slower development of induced or secondary dormancy. Within the range 1.5°‐15°C the rate of loss of innate dormancy appears to be independent of light and is probably independent of temperature. In contrast, the rate of induction of secondary dormancy increases with increase in temperature, and is more rapid in the dark than the light. The rate of induction of secondary dormancy during stratification is greater in R. crispus than in R. obtusifolius. As a consequence, maximum germination was obtained in both species after stratification at 1.5°C in the light, the optimum period of treatment being about 4 weeks in R. Obtusifolius and 6 weeks in R. crispus, while the maximum germination obtained and the optimal period of stratification decrease in both species with increase in stratification temperature.

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