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This study examined germination and dormancy in Galeopsis speciosa (Lamiaceae), a common summer annual weed in cold‐temperate areas. Seeds collected in southern Sweden were subjected to several experiments. The seeds were dormant at maturity. Seeds sown outdoors after collection produced a small number of seedlings that emerged early in the spring. After long cold stratification or stratification outdoors over two winters, the maximum germination was 40–50%; germination occurring over a wide range of temperatures. Warm stratification preceding cold stratification had no effect on germination, but repeated warm and cold periods seemed to promote germination. Gibberellic acid (GA) stimulated germination, but full germination was only achieved after more than 2 months of incubation at the most suitable temperature regime tested. Excised embryos grew and developed into normal seedlings. With these results, the species does not fit into the currently used system for seed dormancy classifications. The response to GA and the growth of excised embryos indicate non‐deep or intermediate physiological dormancy, but dormancy alleviation by stratification was not in line with the guiding principles for these classifications. Galeopsis speciosa has a strong dormancy that is sufficiently alleviated during the winter to allow germination of only part of a seed batch each year; hence a stepwise germination pattern occurs over a period of several years. 相似文献
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Surface soil samples from seven profiles from the central plains of Sudan were investigated using XRD, chemical analysis and Mössbauer spectroscopy measured at 15K. Dioctahedral montmorillonite was the main constituent with different proportions of kaolinite and chlorite. Goethite was found as fine iron oxyhydroxide in all the samples, with haematite detected in two pedons. Crystallinity of the clays was observed to correlate negatively with the amount of free iron oxide in the soil. The influence of the climatic factors on the soil and its formation is discussed. 相似文献
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