The Effects of Temperature on Root Initiation in Detached Cotyledons of Sinapis alba L.

A thermoplate system is described which enables uniformly illuminatedpetri dish cultures to be maintained under a range of temperatureregimes. The system is evaluated and used to investigate theeffects of incubation temperatures between 10 and 35 ?C on rootinitiation. Sinapis cotyledons root most rapidly and in greatest numbersat 25 and 30 ?C. Below 25 ?C, rooting is reduced and delayed,and above 30 ?C rooting is prevented. The optimum temperaturefor initiation of primordia is close to 25 ?C, where, after4 days over 80 per cent of petioles have at least one primordiumand over half of these are already elongating. Initiation isconsiderably reduced at temperatures above 30 ?C and below 25?C and primordium elongation either fails to take place (35?C) or is delayed (20, 13, 10 ?C). At 25 ?C, 90 per cent of the primordia are initiated in theterminal 1.5 mm of the petriole. A similar pattern occurs atother temperatures, but the relative numbers of primordia initiatedin the upper petiole are increased when cotyledons are incubatedat temperatures below 25 ?C. At 25 ?C a higher proportion ofprimordia are initiated in the upper petiole in cotyledons withmany primordia than in cotyledons with few, but the developmentof primordia to the elongation stage is not affected by theirposition in the petiole nor by the numbers of primordia present.