Hrtbur  funt) 
GROWTH  OF  AVENA  COLEOPTILE  AND  FIRST  INTER- 
NODE  IN  DIFFERENT  WAVE-LENGTH  BANDS 
OF  THE  VISIBLE  SPECTRUM 
By  Earl  S.  Johnston, 
Assistant  Director,  Division  of  Radiation  and  Organisms 
Smithsonian  Institution 
INTRODUCTION 
In  a  former  paper  the  author  (1934)  discussed  the  sensitivity  of 
the  Avena  sativa  coleoptile  to  different  wave  lengths  of  Hght  as  mani- 
fested by  phototropic  curvature.  Maximum  sensitivity  occurred  at 
wave  length  4400  A,  with  a  secondary  maximum  at  4750  A.  From 
this  point  the  sensitivity  rapidly  fell  to  a  very  low  value  at  5000  A 
and  gradually  tapered  to  zero  between  5400  and  5500  A.  Beyond 
this  region  and  out  into  the  near  infrared  no  phototropic  response 
was  detected. 
In  the  present  paper  the  results  of  a  growth  study  of  the  oat  coleop- 
tile and  first  internode  '  with  respect  to  different  wave-length  bands 
of  very  weak  light  are  reported.  Data  are  also  presented  on  some 
intensity  effects  of  radiation.  In  all  these  experiments  the  variety 
Markton,  obtained  through  the  kindness  of  T.  Ray  Stanton,  of  the 
United  States  Department  of  Agriculture,  was  used. 
As  mentioned  by  Boysen-Jensen  (1936),  the  elongation  of  the 
first  internode  has  been  attributed  to  numerous  factors  such  as  low 
temperature,  low  soil  moisture  content,  and  high  carbon-dioxide  con- 
tent of  the  atmosphere.  Several  experimenters  have  shown  that  the 
elongation  of  the  first  internode  can  be  suppressed  by  illuminating  the 
seed  when  it  is  in  a  moist  condition.  One  should,  therefore,  expect 
to  obtain  short  first  internodes  on  growing  oat  seedlings  in  light  and 
long  first  internodes  when  they  are  grown  in  darkness.    This  raises 
'According  to  Avery  (1930),  the  elongated  structure  between  the  cotyledon 
and  the  coleoptile  in  oat  seedlings  is  the  first  internode  of  the  axis.  He  regards 
the  term  "  mesocotyl  ",  as  applied  to  this  structure,  meaningless.  The  term  "  first 
internode  "  is  the  author's  preference,  although,  in  discussing  the  work  of  others, 
"  mesocotyl  "  is  sometimes  used. 
Smithsonian  Miscellaneous  Collections,  Vol.  96,  No.  6 
