2  SMITHSONIAN    MISCELLANEOUS    COLLECTIONS  VOL.    96 
effectiveness  of  one  part  of  this  region  over  another  were  masked  by 
the  completeness  of  the  germination. 
In  the  study  of  the  effectiveness  of  radiation  in  the  violet-blue-green 
region  it  had  been  found  that  the  principal  critical  wave  lengths  in 
the  regions  4400  A  and  4800  A  were  identical  (within  the  range  of 
experimental  error)  with  those  reported  by  Johnston  (1934)  and 
others  for  the  phototropic  response  of  oat  coleoptiles.  This  analogy 
suggested  that  similar  pigments  were  involved  in  the  absorption  in 
both  instances,  and  that  the  results  thus  might  well  be  of  significance 
beyond  their  immediate  application  to  the  problem  of  dormancy  in  a 
particular  kind  of  seed.    This  possibility  has  been  made  more  prob- 
4^00  4800     5200  7000  8000 
Fig.  I. — The  action  of  radiation  of  specific  wave-lengths  in  relation  to  the 
germination  of  Hght-sensitive  lettuce  seed.  The  percentages  of  germination  in 
the  spectrum  (immediately  following  an  exposure  to  red  light  sufficient  to  effect 
50%  germination)  are  indicated  as  ordinates,  the  wave-lengths  of  the  spectral 
light  being  indicated  as  abscissae. 
able  through  the  recent  work  of  Burkholder  and  Pratt  (see  Burk- 
holder,  1936,  p.  46),  who  found  not  only  that  radiation  in  the  violet- 
blue  region  influenced  the  movement  of  Mimosa,  but  also  that  a  band 
of  radiation  in  the  7600  A  region  had  a  similar  effect. 
In  view  of  the  foregoing  the  study  of  the  relative  effectiveness  of 
the  wave  lengths  of  visible  radiation  promoting  the  germination  of 
light-sensitive  lettuce  seed  seemed  to  warrant  the  continuation  of  this 
work,  which  led  to  the  results  here  reported. 
REVIEW  OF  LITERATURE 
Cieslar  (1883)  reported  that  yellow  light  favored  the  germination 
of  certain  seeds,  whereas  violet  light  retarded  it.  In  later  years  the 
phraseology  became  more  precise,  with  "  yellow  to  red  "  or  "  yellow, 
orange,  and  red  "  light  as  the  promoting  radiation,  yet  neither  the  wave 
