determination of cardinal temperatures in the seeds of henbane, aconite and hemp

in order to study the cardinal temperatures of three weeds henbane (hyoscyamus niger l), aconite (aconitum napellusl l.) and hemp (cannabis sativa l.) at seven levels of temperatures (5, 10, 15, 20, 25, 30 and 35 °c), an experiment was carried out in completely randomized design with 3 replications and factorial experimental arrangement in weeds research laboratory, faculty of agriculture, ferdowsi university of mashhad in 2012. results showed that the seeds of henbane, aconite and hemp had the maximum germination percentage at 20 c. the response of these weeds to temperatures higher than 20 c was different. hyoscyamus plant had lower germination percentage at 10 c in compare with two others plants. the highest seedling and rootlet length in hemp, henbane and aconite were observed at 20 and 15 c, 30 and 20 c, 20 and 25 c respectively. the cardinal temperatures including base temperature (tb), optimum temperature (to) and ceiling temperature (tc) for henbane was 0.66, 31 and 41 and for aconite 2.84, 11.48 and 41.05 and for hemp 2.6, 26.8 and 42.8 c, respectively. on the whole, results of this experiment showed that there is a wide range of temperatures on germination and emergence of weed for their emergence and establishment.