Wavelength nm

FIG. 5.5. Action spectrum for floral promotion in wheat. After Carr-Smith el al. (1989).

cases a peak in the red part of the spectrum was found together with one at wavelengths greater than 700 nm (Fig. 5.5). In Hyoscyamus, the peak of activity at 710 nm was retained even when given against a background of red light (Borthwick et al., 1969). In Lolium, there was some evidence in a shift of the action maximum to longer wavelengths when a red background was introduced, consistent with the action of phytochrome, although comparative data for only four different wavelengths were presented (Blondon and Jacques, 1970). (Exceptionally, the LDP Calamintha nepe-toides shows maximum sensitivity in red light (as observed for SDP) with no evidence of action beyond 700 nm (Jacques and Jacques, 1989).

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