Fenner, M.2014-06-032014-06-031980-01New Phytologist Volume 84, Issue 1, pages 103–106, January 19800028-646X,1469-8137http://ir-library.ku.ac.ke/handle/123456789/9748DOI: 10.1111/j.1469-8137.1980.tb00752.xThe aim of these experiments was to determine whether exposure to leaf-canopy shade induces a light requirement for germination in Bidens pilosa seeds. Seeds of this species were pretreated by placing them in the shade of a natural canopy for 12 days and then setting half of them to germinate in full light and the other half in darkness. Canopy-treated seeds acquired a marked light requirement. The pretreatment was more effective if the seeds were imbibed during it. Fresh and old seeds gave similar results. In a second experiment the effect of time of exposure to canopy shade on the induction of a light requirement was investigated. It was found that only 1 h exposure to leaf-transmitted light is required to induce an almost complete light requirement in this species. The ecological implications of the results are discussed.enArticle