6  SMITHSONIAN    MISCELLANEOUS    COLLECTIONS  VOL.    96 
The  center  spectrogram  represents  the  absorption  of  an  acetone  extract 
of  seed  pigments.  The  lower  spectrogram  represents  the  emission  of 
the  mercury  arc,  and  provides  a  wave-length  scale  for  the  center  spec- 
trogram. It  is  apparent  from  this  plate  that  the  pigments  absorbing 
the  longer  wave  lengths  of  visible  radiation  in  the  seed  are  similar  to 
those  pigments  found  in  the  leaf  by  Willstatter  and  StoU. 
Since  the  leaf  pigments  absorbing  the  longer  wave  lengths  of  visible 
radiation  are  for  the  most  part  identified  as  chlorophyll,  it  follows 
from  the  data  represented  in  figure  2  and  plate  i  that  (within  the 
limits  of  experimental  error)  the  radiation  most  effective  in  promoting 
germination  in  the  seed  is  that  most  effectively  absorbed  by  chlorophyll 
in  the  same  region. 
Unfortunately,  these  experiments  were  terminated  before  it  was 
possible  to  make  a  positive  identification  of  the  pigments  responsible 
for  the  relatively  intense  absorption  for  wave  lengths  of  radiation 
shorter  than  5400  A  that  is  apparent  on  plate  i.  It  is  certain  that  this 
is  not  due  to  the  blue  absorption  of  chlorophyll  alone,  for  it  is  too 
intense  compared  to  the  red  absorption  and  also  extends  too  far 
toward  the  longer  wave  lengths.  Thus,  the  presence  of  a  yellow  pig- 
ment is  indicated,  and  the  close  agreement  between  the  critical  wave 
lengths  of  radiation  inhibiting  germination  and  those  absorbed  by  the 
carotenes  is  impressive.  However,  a  more  extensive  study  of  the  ab- 
sorption spectrum  of  the  yellow  pigment  found  in  these  seeds  is  neces- 
sary before  more  can  be  said. 
The  close  analogy  between  the  critical  wave  lengths  of  radiation 
influencing  seed  germination  and  the  critical  wave  lengths  of  radiation 
absorbed  by  plant  pigments  places  a  distinct  emphasis  upon  what  is 
perhaps  a  new  and  promising  viewpoint.  In  the  seeds  the  violet-blue 
light  promotes  a  set  of  physiological  responses  quite  different  from  the 
set  which  is  promoted  by  orange-red  light.  It  follows  that  in  green 
plants  the  physiological  response  to  violet-blue  light  may  be  quite  dif- 
ferent from  the  response  to  orange-red  light.  If  such  is  the  case,  the 
study  of  quality  of  light  offers  increasing  promise  in  relation  to  the 
problems  of  photosynthesis,  photoperiodism,  seed  maturation,  seed 
germination,  plant  distribution,  and  so  on. 
In  conjunction  with  an  increasing  interest  in  qualitative  light  effects 
the  results  here  reported  obviously  emphasize  the  desirability  of  a 
more  adequate  knowledge  of  the  quality  of  light  at  the  earth's  surface 
and  of  the  modification  of  that  quality  with  time  of  day  and  year,  with 
latitude,  with  altitude,  and  with  water  vapor  in  the  earth's  atmosphere. 
