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Investigations on seeds of Scrophularia marilandica L. were undertaken to determine their germination requirements. Seeds were collected from three naturally occurring sites and one greenhouse-grown population in London, Ontario in September and October of 1997. Some were set to germinate immediately after collection; others were stored in or on soil outside and/or under controlled laboratory conditions before testing. Germination was assessed under two light/temperature regimes (35°C 14 h light, 20°C 10 h dark and 25°C 14 h light, 10°C 10 h dark), in continuous darkness, and in the presence of two germination-promoting chemicals (GA3 and KNO3). Fresh seeds germinated best at 35/20°C, while stored seeds germinated best at 25/10°C. No differences in percent germination were found among three seed-maturity stages. All chemical treatments, except 0.01 M KNO3, increased percent germination. Significant differences were found both among and within sites for most chemical treatments, but exposure to 3 × 10−4 M GA3 caused almost every seed to germinate. When compared to the control, both the gibberellic acid and the soil-storage treatments contributed to faster germination. Exposure of seeds to naturally prevailing conditions on the soil surface followed by testing under the 25/10°C regime produced the highest percent germination. No seeds germinated in the dark. In summary, seeds of S. marilandica exhibit physiological dormancy, which can be alleviated by exposure to light, after-ripening and/or cold stratification. It is probable that the differences in germination response among sites can be attributed to differences in environmental conditions during seed production. These experiments indicate that the seeds of S. marilandica must be buried shortly after dispersal in order to form a persistent seed bank.

Cypsela dormancy in Scotch thistle (Onopordum acanthium) may be affected by the presence of chemical inhibitors. To investigate this phenomenon, a leachate from O. acanthium cypselas was tested for its ability to inhibit germination of the cypselas from which it was derived (i.e., autoinhibition). Leachates varied in their degree of autoinhibition, depending on the cypsela population from which they were prepared. Overall, removal of leachate from a group of O. acanthium cypselas increased their germinability. Using lettuce (Lactuca sativa) cypselas as an indicator species, bioactivity-guided fractionation was used to isolate a water-soluble, para-substituted benzamide from O. acanthium cypselas, which caused germination inhibition. Various chromatographic, spectroscopic, and spectrometric techniques were applied to the characterization of the bioactive compound.

Germination patterns were studied among three populations of Scotchthistle, Onopordum acanthium L. (Asteraceae). Cypselas(seeds) were collected twice during the growing season for four consecutiveyears (1996–1999) from plants grown in the same location, theEnvironmental Sciences Western Field Station (ESW) near London, Ontario.Cypselas from 1996 came from plants that had been transplanted as rosettes fromtheir original sites to ESW, while those for 1997–1999 came from plantsgrown from cypselas collected in 1996. Fresh cypselas were put to germinate at25 °C, 14 hlight/10 °C, 10 h dark for 55 days.Consistent and significant differences in final germination percentages amongpopulations were obtained over the four years. There were also differencesbetween collections within populations in 1996 and 1998. In addition, the finalgermination percentage (collectively) differed widely among years. There was agreater than 30 percent correlation between germination percentage and meandaily maximum temperature during cypsela maturation. Since there were similardifferences among populations every year, it appears that germination patternsof O. acanthium populations have a genetic basis as wellasan environmental one.