Studies in Vernalisation of Cereals

The photoperiodic reactions of spring rye and vernalised and unvernalised winter rye have been studied in detail and interpreted in terms of a schema presented in earlier papers. Vernalisation treatments ranging from 0 to 13 weeks were used and three daylengths (continuous light, C.L.; normal days, L.D.; 10-hr. days, S.D.), and the interaction effects of these factors were studied on the following developmental features: time to initiation of flowering and to ‘double-ridge’ formation; progress of differentiation and growth rate of the apex of the main shoot before and after initiation. Systematic dissections of the apex were carried out to obtain data for this study. The validity of the concept of ‘minimal leaf number’ was re-examined and confirmed by using dwarf embryos with subnormal numbers of primordia at germination. Unvernalised winter rye was shown to behave as a short-day plant before flower initiation since photoperiodic induction by short days is annulled by interrupting the dark period by a short light period at low intensity. The effect of exposure of a single leaf to continuous light, while the remainder of the plant was kept in short days, has been shown to be transmitted to the apex and hastens both flower induction and spikelet development in fully vernalised rye. Vernalised winter rye and spring rye thus behave as long-day plants.