Dark Red Far-red Figure 9-2 数 FIGURE 17.2 Lettuce seed germination is a typical photore- versible response controlled by phytochrome. Red light promotes lettuce seed germination, but this effect is reversed by far-red light. Imbibed(water-moistened)seeds were given alternating treatments of red followed by far red light. The effect of the light treatment depended on the Red Far-red Red Red Far-red Red Far-red last treatment given. (Photos O M B. Wilkins.Figure 9-2