WAVE LENGTHS OF RADIATION IN THE VISIBLE 



SPECTRUM INHIBITING THE GERMINATION 



OF LIGHT-SENSITIVE LETTUCE SEED 



By lewis H. flint 



Division of Seed Investigations, Bureau of Plant Industry, 



U. S. Department of Agriculture 



E. D. McALISTER 



Division of Radiation and Organisms, 

 Smithsonian Institution 



IXTRODUCTIOX 



In studies of the light-sensitivity of " dormant " lettuce seed previ- 

 ously reported (3)' it was noted that radiation of the longer wave 

 lengths of visible light, characterizing the colors yellow, orange, and 

 red, promoted germination, whereas radiation of the shorter wave 

 lengths of visible light, characterizing the colors violet, blue, and green, 

 inhibited germination. The material appeared to be unusually well 

 adapted to the study of response to radiation, and steps were taken 

 to establish the relative effectiveness of radiation of various wave 

 lengths with respect to the germination of the seed. 



While these studies were in progress, Johnston (6) at the Smith- 

 sonian Institution reported the results of a careful series of measure- 

 ments of phototropic response of the etiolated oat coleoptile, which 

 emphasized the fact that the shorter wave lengths of visible light were 

 responsible for such bending. He interpreted this activity as due to 

 an inhibitory effect of the shorter wave lengths upon the cells exposed 

 to such radiation. 



On account of the obvious analogy between the results obtained 

 with the shorter wave lengths of light in respect to inhibition in 

 germination and in phototropism the facilities of the two research 

 divisions were combined in the furtherance of the germination study, 

 the cooperative investigation leading to the results here presented. 



^ Numbers in parentheses refer to list of literature cited, at the end of this 

 paper. 



Smithsonian Miscellaneous Collections, Vol. 94, No. 5 



I 



