Germination and Persistence of Achenes of Scotch Thistle

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Abstract
Achenes of Scotch thistle(Onopordum acanthiumL.) contain a water-soluble germination inhibitor and are sensitive to differences in light quality. Germination of these achenes can be enhanced by the addition of 0.14 mmole of gibberellic acid and 1.0 mmole of potassium nitrate to the substrate. Dissected embryos exhibit germination responses similar to those observed for achenes. Naturally-distributed achenes recovered from the soil in the field increased in germination under fluorescent light and after washing. Achenes will not germinate on the surface of a constant-moisture-supplying substrate when exposed to an unsaturated atmosphere. The physical environment of the seedbed apparently is paramount in controlling germination and persistence of achenes of Scotch thistle.