Flowering behaviour of populations of Dactylis glomerata under field conditions in Britain.
Twenty-one agronomic varieties and local populations of D. glomerata ssp. euglomerata and two of ssp. lusitanica from a wide range of habitats were studied. In most populations some of the plants head in the year of sowing; "the wild populations, and those from areas of less severe winters, tend to head more freely". Spring heading date varies between populations and appears to be controlled by genetic differences in the daylength required for the elongation of the culms. In some populations inflorescences can be initiated throughout the winter, suggesting that initiation has a lower daylength threshold than has elongation of the culm. In many populations, a high proportion of the plants produce heads in the aftermath growth after cutting; heading in the year of sowing and in the aftermath are correlated. The results are discussed in relation to climatic adaptation and the heading behaviour of populations grown in other climates. [Cf. XXXIV, 5928].