NO.    2         IRRADIATED    LETTUCE    SEED FLINT    AND    McALlSTER  3 
length  range  nor  the  relative  effectiveness  of  bands  of  radiation  within 
the  range  were  established.  Flint  ( 1934)  reported  that  the  upper  limit 
of  the  radiation  inhibiting  germination  was  at  about  5200  A,  while  the 
upper  limit  of  the  seemingly  analogous  phototropic  response  was  set 
as  about  5400  A  by  Johnston  (1934).  The  curves  of  the  absorption 
spectra  of  carotin  and  xanthophyll  as  reported  by  McNicholas  (1931) 
reach  low  points  in  the  region  5000  A  to  5500  A,  with  principal  criti- 
cal wave  lengths  of  maximum  absorption  at  about  4400  A  and  4800  A 
(when  allowance  is  made  for  the  shift  in  wave  length  associated  with 
the  solvent).  These  correspond  closely  with  the  regions  of  maximum 
effectiveness  of  this  radiation  in  inhibiting  germination  and  inducing 
phototropism.  The  curves  of  the  absorption  spectra  of  the  chlorophylls 
as  given  by  Zscheile  (1934)  are  uniformly  low  in  the  green  region 
and  Shuck  (1935)  has  held  that  there  was  a  band  of  this  radiation 
which  had  no  effect  on  germination.  On  the  other  hand  the  curve  of 
the  action  of  radiation  of  specific  wave  lengths  in  relation  to  the  germi- 
nation of  light-sensitive  lettuce  seed  as  developed  in  the  work  of  Flint 
and  McAlister  (see  fig.  i)  indicates  an  immediate  transition  of  reac- 
tion in  this  region,  though  not  as  abrupt  a  change  as  that  taking  place 
at  the  long  wave  length  end  of  the  promoting  influence  at  about  7000  A. 
Kommerell  (1927),  in  studying  quality  of  light  and  germination, 
had  concluded  that  at  any  specified  wave  length  the  effectiveness  of 
the  radiation  was  proportional  to  the  energy  falling  upon  the  surface 
of  the  seed.  The  work  of  Flint  and  McAlister,  on  the  other  hand, 
indicated  that  the  effectiveness  of  the  radiation  was  proportional  to 
its  absorption  by  the  seed  pigments.  The  investigations  of  Meischke 
(1936)  support  the  latter  viewpoint. 
METHODS 
The  procedure  and  apparatus  used  in  this  investigation  was  essen- 
tially that  described  in  detail  in  a  previous  paper  (Flint  and  McAlister, 
1935)  except  that  blue  light  of  controlled  intensity  was  superimposed 
uniformly  over  the  spectral  region  in  which  the  seeds  were  being 
treated.  By  the  well-known  system  of  trial  and  error,  using  constant 
continuous  spectral  illumination,  the  blue  light  was  so  regulated  in 
intensity  that  the  maximum  germination  throughout  the  set  of  com- 
partments in  24  hours  was  precisely  100  percent  in  some  one  com- 
partment. With  compartments  0.4  inch  wide  as  used  in  the  experiments 
previously  reported,  the  conditions  were  then  such  that  any  increase 
in  the  intensity  of  the  blue  radiation  gave  less  than  100  percent  ger- 
mination in  this  compartment.    All   experiments   reported   were   at 
