Dormancy and impotency of cocklebur seeds II. Phase sequence in germination process

Interactions of C₂H₄, CO₂, O₂ and high temperature in stimulatinggermination of cocklebur (Xanthium pennsylvanicum Wallr.) seedswere studied and the phase sensitive to each factor during germinationwas determined. The combination of CO₂ and enriched O₂, andparticularly that of C₂H₄ and enriched O₂, much more effectivelystimulated germination than CO₂ and C₂H₄. At low temperature,however, the cooperation of CO₂ and enriched O₂ was lost andonly the effect of C₂H₄ in combination with CO₂ or enrichedO₂ remained. Carbon dioxide stimulated C₂H₄ production and induced germinationwhen it was applied in the first period of water imbibition,corresponding to the passive thrust forming phase. C₂H₄ becameeffective after the CO₂-responsive phase. In contrast, bothO₂ enrichment and high temperature became increasingly effectivewith the imbibition times. Anaerobiosis applied during the firstperiod of the germination process showed no inhibitory effect,whereas CO₂ and C₂H₄ were stimulative even under such a condition. (Received August 26, 1974; )