Abstract. The effect on seed germination of the red/far-red ratio of light (ζ) as modified by a leaf canopy was studied. The artificial light sources used and daylight filtered through leaves appeared to have identical effects in tests with lettuce seed.
The sensitivity of the seeds to ζ varied with the environmental conditions during pretreatment and during the actual germination test. Freshly harvested and dry-stored seeds of Cirsium palustre were strongly inhibited at low ζ; after stratification, the inhibition was much less. The fact that C. palustre emerges mainly after the coppice is felled could not be explained from these results combined with field data on ζ and the response of germination to temperature.
The ecological significance of inhibition at low ζ is to be found directly after dispersal. Seed germination will then be delayed until the following spring or later.
Geum urbanum showed primary dormancy, which was released by a stratification treatment. No inhibition of germination at low ζ was found in the spring and seeds germinated in light and darkness at low temperatures. These results explain why the species emerges early in spring regardless of the presence of the ash canopy.