Spores of the fern Pteris vittata did not germinate under total dark conditions, while an exposure of the spores to continuous white light brought about germination. The germination was most effectively induced by red light and somewhat by green and far-red, but not at all by blue light. The sensitivity of spores to red light increased and leveled off about 4 days after sowing at 27–28°. The promoting effect of red light could be brought about by a single exposure of low intensity. Far-red light given immediately after red light almost completely reversed the red light effect, and the photoresponse to red and far-red light was repeatedly reversible. The photoreversibility was lost during an intervening darkness between red and far-red irradiations, and 50% of the initial reversibility was lost after about 6 hr of darkness at 27–28°. These observations suggest that the phytochrome system controls the germination of the fern spore. When the imbibed spores were briefly exposed to a low-energy blue light immediately before or after red irradiation, their germination was completely inhibited. The blue light-induced inhibition was never reversed by brief red irradiation given immediately after the blue light. The escape reaction of red light-induced germination as indicated by blue light given after various periods of intervening darkness was also observed, and its rate was very similar to that determined by using far-red light. Spores exposed to blue light required 3 days' incubation in darkness at 27–28° to recover their sensitivity to red light. The recovery in darkness of this red sensitivity was temperature-dependent. It is thus suggested that an unknown bluelight absorbing pigment may be involved in the inhibition of phytochrome-mediated spore germination.
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Sugai et al. (1967) studied this question.