NO. 
IRRADIATED    LETTUCE    SEED FLINT    AND    McALISTER 
the  5000-6000  A  range  has  not  been  established  in  these  trials,  but  in 
its  entirety  this  radiation  is  obviously  far  less  effective  than  that  in  the 
6700  A  region. 
DISCUSSION 
The  results  given  in  table  i  have  been  averaged  and  represented 
graphically  as  the  full  line  curve  in  figure  2. 
It  is  obvious  from  this  diagram  that  the  radiation  most  effective  in 
promoting  the  germination  of  the  seed  had  a  wave  length  of  the  order 
of  6700  A.   The  nature  and  position  of  this  curve  invites  comparison 
iy/)V£  LENGTH  W  ANOSr/iOMS 
Fig.  2. — Curves  of  seed  response  and  chlorophyll  absorption. 
with  the  curve  of  the  absorption  spectrum  of  the  chlorophylls  in  this 
region,  and  the  analogy  is  impressive.  Here  is  an  instance,  then,  in 
which,  within  the  limits  of  experimental  error,  the  apparent  critical 
wave  length  of  radiation  promoting  germination  coincides  with  the 
major  absorption  in  this  region  by  a  pigment  common  to  all  green 
plants.  The  approximate  order  of  correspondence  is  indicated  in  fig- 
ure 2.  In  Zscheile's  work  the  leaf  pigments  were  extracted  with  ether. 
In  the  germination  study  the  seed  pigments  were  acting  in  their  natural 
environment,  which  was  an  aqueous  solution.  Under  these  circum- 
stances the  wave  length  shift  apparent  in  figure  2  is  about  the  amount 
to  be  expected. 
In  plate  i  the  upper  spectrogram  is  taken  from  Willstatter  and  StoU 
and  represents  the  absorption  of  an  acetone  extract  of  leaf  pigments. 
