Germination of the Bluebell (Hyacinthoides non-scripta (L.) Chouard) in Relation to its Distribution and Habitat

Studies of germination response to temperature and measurements of meteorological conditions in the field were made with populations of Hyacinthoides non-scripta growing in two places in south-eastern England. Seeds did not germinate when sown directly at temperatures over the range 6° to 31 °C. Germination occurred in response to a two phase treatment (a) a high temperature conditioning phase with an optimum at 26° to 31 °C; (b) a germination phase at 11 °C. No response was found to a low temperature conditioning phase equivalent to winter chilling. Soil temperature measurements during late summer and autumn showed that these were generally below the optimum for the conditioning phase, but nevertheless within the range at which changes leading to germination did occur. The results suggested that germination occurs naturally as temperatures fall to c. 11 °C in late autumn and that seedlings overwinter and grow whenever periods of mild weather permit. (Young seedlings were identified in the field in late November.) A residue of ungerminated seed may overwinter as an insurance against loss of overwintering seedlings. The proportion of dormant seed to germinated seedlings appears to be critically dependent on temperature and may vary from year to year, site to site or position within a site. An examination of meteorological data suggested that the natural distribution of the species is defined by the mean daily minimum temperature of the coldest winter month (> 0 °C) and the mean daily maximum temperature of the warmest summer month (< 25 °C). The germination responses identified appear to provide a finely balanced mechanism which affords maximum insurance on established sites and maximum opportunism in the colonization of new sites.