10 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 94 



In resume, the results obtained with the Wratten filters, taken in 

 conjunction with the curve of violet-blue-green inhibition given by 

 the spectral data and with the newly discovered inhibitory influence in 

 the 7600 A region, make it more than ever obvious that the effects ob- 

 tained through the use of any color filter may not safely be interpreted 

 without an analysis of its spectral transmission. 



The results presented in this paper indicate the general relative 

 effectiveness of radiation of various wave lengths in the visible spec- 

 trum found to inhibit the germination of light-sensitive lettuce seed. 



3800 4000 -4200 4400 4600 4800 5000 



Fig. 5. — Curve of inhibition in the violet-blue-green region compared with 

 the curve of phototropic response of oat coleoptiles obtained by Johnston. Heavy 

 line represents the inhibition; dotted line the phototropic response. 



Further studies designed to yield quantitative results as to the relative 

 effectiveness of both promoting and inhibiting radiation are now in 

 progress. 



SUMMARY 



Announcement is made of the discovery of a band in the region of 

 7600 A which inhibits the germination of light-sensitive lettuce seed 

 far more effectively at the energies characterizing both solar and 

 Mazda radiation (in this region) than do similar inhibitory influences 

 previously noted in the regions 4200 A to 5200 A. 



The relative effectiveness of radiation in the violet, blue, and green 

 regions of the spectrum — at 4200 A to 5200 A — in inhibiting germina- 

 tion in light-sensitive lettuce seed is found to be the same as its relative 



