| Abstract: | The results of pilot experiments lead to the conclusion thatD. glomerata exhibits a number of developmental stages: firstly,a juvenile stage during which the plant is insensitive to environmentalconditions which later stimulate flowering; secondly, an inductivestage, when the plant responds to periodic exposure to darknessat the conclusion of which it is fully induced or ripe to flower,and finally, a post-inductive stage during which inflorescencesare initiated and undergo further development; these are long-dayprocesses. In four populations studied the juvenile stage lasts about fiveweeks. In north European material daily exposure to seven hoursof darkness is near the minimum for induction although thereis considerable within-population variation. Further, it appearsthat the daily dark requirement becomes less as the plant ages. Comparisons are made of the flowering behaviour of D. glomerataand Lolium perenne. The differences between these species resultfrom the presence of a juvenile stage in Dactylis and the possibilityof satisfying its inductive requirement by long days. Inductionin Lolium requires short days or low temperature. The significance of these results is discussed in the lightof previous work on the environmental control of flowering inherbage grasses. The existence of three developmental stagescan explain the wide differences in interpretation of the floweringrequirements of Dactylis previously held. The possible evolutionof flowering requirements is also discussed. |
