PHOTOPERIODISM IN SEEDS AND BUDS 75 



mfji, at intervals of approximately 50 m/j. between peaks. The source 

 used was a 500-watt tungsten filament lamp. In order to eliminate the 

 possibility of the transmittance of an appreciable quantity of infrared 

 radiation, copper sulfate gelatin filters were used in conjunction with 

 the blue interference filters. It was arranged that the energy level at the 

 position of the seeds was the same (50 or 80 /xw/cm^) for each spec- 

 tral region. It was found that Nemophila seed is inhibited by blue light 

 (i.e., with filters peaking at 452, 483, and 496 m/j.), but only slightly 

 inhibited under the filters peaking at 542, 547, 596, and 651 m/x. The 

 inhibition is very strong in the far red, at 710 m/x, and somewhat less 

 at 760 mix. 



The possibility that the blue region was inhibitory because of "stray" 

 far-red radiation seems to be excluded by the observation that similar 

 inhibition could be obtained by using as a source blue fluorescent tubes 

 in conjunction with blue Perspex (B.705) and 1-cm screen of M/3 

 copper chloride. The latter would effectively remove any small com- 

 ponent of far-red radiation emitted by the tubes. In spite of this, the 

 seeds were strongly inhibited by light from this source, which covered 

 the band from 400 to 520 mix. Thus, seed of Nemophila is inhibited 

 not only by a far-red region, but also by blue light. These results agree 

 very well with those of Restihr (1939) for Phacelia tanacetijoUa. The 

 inhibitory effect of far red is considerably greater than that of blue. 

 Thus, a 4-hr daily photoperiod of far red brings about almost com- 

 plete inhibition of Nemophila seed, whereas 1 6- to 20-hr photoperiods 

 are required with blue radiation even at "saturating" intensities. 



In view of the markedly inhibitory effect of blue in Nemophila it was 

 decided to reinvestigate the reported effects of blue in lettuce seed. 

 Flint and McAlister (1935) reported inhibitory effects of long periods 

 of irradiation with blue light on lettuce seed. They exposed the seeds 

 first to a short period of red light, sufficient to induce 50% germina- 

 tion, and then exposed them for 48 hr to various spectral regions. They 

 found inhibition in the blue region and published a detailed action 

 spectrum for this effect. Borthwick et al. (1954), apparently using 

 short periods of irradiation, also reported both stimulation and inhibi- 

 tion of germination by blue alone, but the effects were not great. They 

 found that maximum sensitivity for the promotive effect occurred at 

 1 2-20 hr of imbibition, and maximum sensitivity for inhibition after 



