4  SMITHSONIAN    MISCELLANEOUS    COLLECTIONS  VOL.    96 
agreement  between  the  duplicate  experiments  of  the  exposed  series. 
The  greatest  discrepancies  occur  for  wave  lengths  5195  A  and  5403  A. 
In  the  dark  series  of  experiments  there  is  considerable  variation  be- 
tween the  averages  of  similar  experiments.  This  is  especially  notice- 
able for  those  corresponding  to  wave  lengths  4050  A,  4405  A,  and 
5403  A.  For  example,  there  appears  to  be  no  good  reason  why  the 
dark  experiments  corresponding  to  those  of  wave  length  4405  A 
should  give  an  average  for  the  first  internode  of  59  mm  in  one  case  and 
34  mm  in  the  other.  The  temperature  ranges  were  exactly  the  same, 
76°— 75°  F.  There  is  the  possibility  that  the  filter  paper  medium  here 
used  was  drier  in  one  experiment  than  in  the  other.  The  dark  controls 
of  the  first  nine  experiments  were  in  a  different  container  than  those 
of  the  exposed  series.  It  would  appear  from  this  example  and  general 
observations  throughout  all  the  experiments  that  individual  variations 
are  enhanced  when  the  oat  seedlings  are  grown  in  the  absence  of  light. 
The  growth  data  of  table  i  are  diagrammatically  represented  in 
figure  2.  The  ordinates  represent  length  in  millimeters.  Similar 
experiments  are  grouped  together  with  the  wave  length  designated 
below.  In  the  series  exposed  to  fight  the  first  internodes  are  repre- 
sented by  the  dotted  sections  and  the  coleoptiles  by  the  clear  sections. 
In  the  dark  series  the  shaded  portions  represent  the  first  internodes 
and  the  hatched  portions  the  coleoptiles. 
The  most  striking  feature  of  this  diagram  is  that  for  all  wave 
lengths  the  first  internodes  of  the  exposed  plants  are  always  shorter 
than  the  first  internodes  of  the  corresponding  dark  control  plants. 
There  is  not  a  single  experiment  in  which  this  is  not  the  case.  Even 
in  wave  length  7600  A,  which  was  scarcely  visible  to  the  eye,  the 
lengths  of  the  first  internodes  of  the  exposed  plants  are  depressed. 
Data  from  experiments  not  shown  here  but  carried  out  several 
months  earlier,  covering  the  range  of  wave  lengths  whose  average 
was  7600  A,  were  very  similar  to  those  here  presented.  Another 
feature  that  this  diagram  clearly  shows  is  that  the  coleoptiles  of  all 
the  dark  experiments  are  short  in  comparison  to  the  coleoptiles  in  the 
exposed  series.  Here  again  there  are  no  exceptions.  Furthermore 
at  the  end  of  the  4-day  periods  the  total  length  of  seedlings  in  the 
dark  series  of  experiments  is  somewhat  greater  than  the  total  length 
of  seedlings  in  the  exposed  series.  There  are  a  few  exceptions.  The 
average  total  length  of  seedlings  in  the  former  group  is  but  7  mm 
greater  than  the  total  length  of  the  latter  or  exposed  group.  This 
would  indicate  that  the  total  growth  attained  in  a  4-day  period  was 
not  greatly  influenced  by  light.  If  growth  depends  on  the  amount 
of  growth  substance  present,  it  would  indicate  that  light  of  this  low 
