NO.    6  GROWTH    OF    AVENA    COLEOPTILE JOHNSTON  3 
A  set  of  similar  seeds  was  grown  simultaneously  in  darkness  for 
the  entire  period  of  four  days.  In  the  first  nine  experiments  the 
dark  controls  were  grown  in  a  separate  container.  For  the  other 
experiments  of  this  series  the  dark  controls  were  grown  in  the  same 
container  with  the  illuminated  plants  but  were  separated  from  them 
by  a  black  paper  partition  held  between  two  pieces  of  glass.  The 
top  of  the  chamber  was  covered  with  a  piece  of  glass  and  the  entire 
top  area,  as  well  as  the  sides,  covered  with  black  paper  and  cloth, 
except  for  the  opening,  which  permitted  light  to  reach  the  exposed 
set  of  plants.  Subsequent  experiments  showed  that  even  these  pre- 
cautions to  keep  light  from  reaching  the  dark  control  plants  failed. 
Examination  of  data  in  table  3  clearly  shows  that  the  dark  controls 
in  the  same  chamber  with  the  exposed  plants  must  have  received  some 
scattered  light  because  of  their  differences  in  growth.  Because  of  this 
scattered  light  effect  the  dark  controls  with  the  exception  of  the 
first  nine  experiments  in  the  first  series  are  of  little  value. 
An  experiment  for  each  wave-length  setting  was  repeated  at  least 
once.  At  the  end  of  each  4-day  experiment  the  lengths  of  coleoptiles 
and  first  internodes  were  determined.  Because  of  the  restricted  size  of 
the  light  beam  coming  from  the  monochromator  the  number  of  seeds 
exposed  was  limited  to  about  seven  without  too  great  crowding. 
Occasionally  a  seed  or  two  failed  to  germinate,  and  sometimes  some- 
thing happened  that  justified  the  elimination  of  others.  For  the  entire 
series  of  experiments  the  average  number  of  seedlings  in  each  ex- 
posed group  and  each  dark  control  was  six.  Since  each  experiment  was 
repeated,  this  at  least  doubled  the  number  of  seedlings  for  each  wave- 
length setting. 
The  experiments  were  conducted  in  a  small  room  with  no  outside 
walls.  The  lamp  was  located  in  another  room,  so  that  after  an  ex- 
periment was  started  no  entrance  was  made  to  this  room  until  its 
conclusion  at  the  end  of  four  days.  Because  of  the  location  of  this 
room  in  the  basement  of  the  Smithsonian  Building,  the  temperature 
variation  was  exceedingly  small.  Seldom  was  the  difference  between 
maximum  and  minimum  temperature  greater  than  2°  F.  for  any 
of  the  4-day  periods.  Once  there  was  a  4°  difference  and  twice  a  3° 
difference.  The  average  maximum  and  minimum  temperatures  for 
the  36  different  experiments  were  75°  F.  and  74°  F.,  respectively. 
The  average  lengths  (mm)  of  the  first  internode,  coleoptile,  and 
total  oat  seedling  of  each  4-day  experiment  are  presented  in  table  i. 
For  each  wave  length  the  data  of  at  least  two  experiments  are  given. 
The  last  two  columns  show  the  maximum  and  minimum  temperatures 
(°  F.)  for  each  experiment.   It  will  be  noted  that  there  is  fairly  good 
