Abstract
1) Red light irradiated for a relatively short time to Pharbitis plants grown under continuous green, blue, or far-red lights and in darkness just before a 16 hr dark treatment always initiated flowering induction, but far-red light given in the same way to red light grown plants inhibited flowering induction.
2) The effectiveness of red light given to plants grown under green light before a 16 hr dark treatment to induce photoperiodic sensitivity was compared between fluorescent light obtained from colored fluorescent lamps and spectral light beams from a grating spectrograph.
3) The effectiveness in inhibiting flowering induction of far-red light, obtained through an IR-1 filter and radiant heat cut glass from incandescent lamps, was also compared with that of spectral light beams from the far-red region by irradiating to plants grown under red light for a short time before the dark period.
4) Total energy values required for inducing 100% flowering by red light were about 37×106 erg/cm2 and 8.9×106erg/cm2 in fluorescent and spectral light, respectively.Those required for complete inhibition of flowering were 8.6×106 erg/cm2 and 9.9×104 in filtered far-red light and spectral light, respectively.
The present experiment indicates that the total energy required for the same photoresponse are apt to be larger in colored fluorescent lights or filtered lights than in spectral light beams.This fact must be considered in photobiological experiments using monochromatic light other than spectral light beams.
5) The regions effective for flowering induction are roughly the three regions with wavelengths of about 550-600 nm, 620-640 nm and 650-675 nm, and those for inhibition of flowering induction range from about 710 nm to 770nm.
6) Experimental conditions for light and temperature were examined in detail. Reasons for the difference in total energy values between fluorescent light and spectral light were discussed.
