NO. 5 IRRADIATED LETTUCE SEED FLINT AND McALISTER / 



lengths to which seeds were exposed. With the apparatus and pro- 

 cedure described in the foregoing section such results as those given 

 in figure 3 were obtained in the long red region. 



Such results as those presented in figure 3 established the presence 

 of a strong inhibitory influence in the region of 7600 A. 



By applying the same methods to the violet, blue, and green regions 

 of the spectrum, such results as those presented in figure 4 were 

 obtained. 



In conjunction with the foregoing experiments a study of ether 

 extracts of lettuce seed was carried, out. These extracts contained 

 oil and pigments. Definite absorption in the region 4200 A to 5200 A 

 was evidenced by the transmission curves. These remained bimodal, 

 even after appreciable oxidation had taken place, and thus appeared 

 suggestive in relation to the bimodal curve of inhibition given in 

 figure 4. Definite absorption in the region 5200 A to 7000 A was also 

 evidenced by the transmission curves, suggesting the presence of some 

 precursors of chlorophyll and allied pigments. No appreciable ab- 

 sorption in the region 7600 A was noted. 



DISCUSSION 



The discovery of a strong inhibitory influence in the region of 

 7600 A, although made in an effort to explain the difference in the 

 response to the light transmitted by certain green Wratten filters, and 

 quite incidental to the study of the precise nature of the curve of 

 inhibition in the regions characterizing violet, blue, and green light, 

 may well transcend in importance the original objective of the coopera- 

 tive studies. Since this discovery appears to offer a clearer approach 

 to biological problems involving light, it has been given precedence in 

 these considerations. 



All the green Wratten filters used by Flint (3) were found to trans- 

 mit in the 7600 A region, but the two filters transmitting light which 

 promoted germination had such a low transmission in this region that 

 the eft'ects of the promoting regions — the yellow, orange, and red — 

 predominated over the effects of the inhibiting regions — the long red, 

 the violet, the blue, and the green. Since many blue and violet glass, 

 liquid, or gelatin filters transmit in the region 7600 A, it follows that 

 the newly discovered inhibitory band becomes a potential source of 

 confusion as to the effectiveness of radiation in the more visible spec- 

 trum with respect to the germination of light-sensitive lettuce seed. 

 Moreover, since the same type of light-sensitivity has been recognized 

 as characterizing other seeds, this factor may well be of some general 

 significance with respect to light-sensitivity in seeds. 



