WAVE  LENGTHS  OF  RADIATION  IN  THE  VISIBLE 
SPECTRUM  PROMOTING  THE  GERMINATION 
OF  LIGHT-SENSITIVE  LETTUCE  SEED 
By  lewis  H.  flint,' 
Boycc  Thompson  Institute  for  PlatH  Research,  Inc. 
AND 
E.  D.  McALISTER. 
Dk'isifln  of  Radiation  and  Organisms, 
Smithsonian  Institution 
(With  One  Plate) 
INTRODUCTION 
The  purpose  of  this  investigation  is  to  fix  definitely  the  wave  lengths 
of  radiation  which  maximally  promote  the  germination  of  light-sensi- 
tive lettuce  seed  °  and  to  study  their  relationships  to  the  wave  lengths 
of  radiation  most  effective  in  other  fundamental  plant  phenomena. 
In  a  previous  publication  (Flint  and  McAlister,  1935)  the  wave 
lengths  of  radiation  in  the  visible  spectrum  inhibiting  the  germination 
of  light-sensitive  lettuce  seed  were  reported  as  occurring  in  two  re- 
gions: one  in  the  violet-blue-green  region  (with  principal  maxima  at 
about  4400  and  4800  angstroms),  and  the  other  in  the  red-to-near- 
infrared  region  (with  one  maximum,  at  about  7600  angstroms).  The 
earlier  work  of  Flint  (1934,  a,  b)  had  indicated  the  general  range  of 
the  radiation  promoting  germination  as  5200  to  7000  A,  but  the 
curve  of  relative  efi^ectiveness  of  the  radiation  within  this  range  was 
unknown.  The  accompanying  graph  (fig.  i),  reproduced  from  a  re- 
cent paper  by  Flint  and  McAlister  (1936),  illustrates  the  state  of  the 
study  of  radiation  in  relation  to  the  germination  of  this  particular  seed 
at  the  beginning  of  the  researches  here  reported  for  the  same  material. 
It  may  be  noted  from  figure  i  that  at  the  intensities  of  radiation 
applied  in  the  region  5200-7000  A  a  germination  of  100  percent  was 
secured  at  the  longer  wave  lengths.    It  follows  that  differences  in  the 
'  Formerly  of  the  Division  of  Seed  Investigations,  Bureau  of  Plant  Industry, 
U.  S.  Department  of  Agriculture. 
'  Light-sensitive  Arlington  Fancy  lettuce  seed  was  used  throughout  the  co- 
operative researches. 
Smithsonian  Miscellaneous  Collections,  Vol.  96,  No.  2 
