SEED GERMINATION 



525 



Rapids at 30°C, germination is an inverse function of light intensity 

 (125, 250, 500 ft-c). The lower the light intensity, the greater the 

 stimulation above the dark germination. At lower temperatures there 

 is no difference between the different light intensities, since maximum 

 germination is obtained with all. The same inverse relation was observed 

 for var. Black Seeded Simpson and var. Oak Leaf at 24:°C. For Oak Leaf 

 there was a stimulation of germination at 15, 35, and 75 ft-c (inversely 

 proportional to the intensity of the light) and an inhibition at 130 ft-c 

 of the percentage of germination compared with dark germination. 



Quality of Light. Cieslar (1883) first reported for the positively photo- 

 blastic Poa pratensis that yellow light acts like white light, blue light like 



4000 4500 5000 5500 6000 6500 7000 7500 8000 



Fig. 11-1. Action spectrum for (a) Amaranthys {after Resiihr, 1939a); (b) Phacelia 

 {after Resiihr, 1939a); and (c) Lactuca {after Flint and McAlisler, 1935, 1937). 



I;::"-':! - stimulation 



III III = INHIBITION 

 INDIFFERENT 



darkness. Kinzel (1913-1926) found, in general, that most positively 

 photoblastic seeds were stimulated by light of longer wave length and 

 inhibited by light of shorter wave length. But he also cites some cases 

 in which yellow light stimulates most (e.g., Veronica peregrina). Many 

 other authors also found that the effect of red light is like that of white, 

 the effect of blue like that of darkness (e.g., Ernst, 1906; Haack, 1906; 

 Toole, 1938; Eliason and Heit, 19-40). Since the most extensive and most 

 accurate work was done with Phacelia, Amaranthus, and Lactuca, we will 

 deal chiefly with these plants. Figure 11-1 gives a comparison of the 

 inhibiting, stimulating, and indifferent wave lengths for these plants, 

 according to Flint and McAhster (1935, 1937) and Resiihr (1939a). The 

 most remarkable point is the similarity of the stimulating and inhibiting 

 wave lengths, although Lac^wca is positively and Phacelia and Amaranthus 

 negatively photoblastic. This was pointed out for the first time by 

 Meischke (1936) for five positively and eight negatively photoblastic 

 species. 



For all three there are two zones of inhibiting light, one around 4400 A 

 and one around 4800 A. For Lactuca and Amaranthus there is another 

 inhibiting region in the near infrared. For Phacelia this region is moved 

 to the visible red. There is a stimulating zone for all three around 

 6400 A, which i or Lactuca extends up to 7100 A. Resiihr (1939a) desig- 



