NO.    2         IRRADIATED    LETTUCE    SEED FLINT    AND    McALISTER  7 
SUMMARY 
Radiation  of  wave  lengths  ranging  from  about  5200  A  to  about 
7000  A  characterizing  the  colors  yellow,  orange,  and  red,  promotes  the 
germination  of  light-sensitive  lettuce  seed ;  but  within  this  range  the 
longer  wave  lengths  are  by  far  the  most  effective. 
The  critical  wave  length  of  the  radiation  promoting  germination 
within  the  most  effective  range  is  approximately  6700  A. 
Within  the  limits  of  experimental  error  the  radiation  most  eflFective 
in  promoting  germination  is  that  most  abundantly  absorbed  by  chloro- 
phyll in  the  same  region. 
The  absorption  characteristics  of  an  acetone  extract  demonstrate  the 
presence  of  chlorophyll  in  the  seed. 
LITERATURE  CITED 
BURKHOLDER,    PaUL   R. 
1936.    The  role  of  light  in  the  life  of  plants.    Bot.  Rev.,  no.  i,  pp.  1-52,  and 
no.  3.  pp.  97-168. 
ClESLAR,    AdOLPH 
1883.    Untersuchungen  iiber  den  Einfluss  des  Lichtes  auf  die  Keimung  der 
Samen,  pp.  270-295. 
Flint,  Lewis  H. 
1934  a.  Light    in    relation   to    dormancy    and    germination    in    lettuce    seed. 
Science,  vol.  80,  pp.  38-40. 
1934  b.  Light-sensitivity   in   relation   to  dormancy   in   lettuce   seed.    Compt. 
Rend.  Assoc.  Internat.  Ess.  Sem.,  Copenhagen. 
Flint,  Lewis  H.,  and  McAlister,  E.  D. 
1935-    Wave   lengths    of    radiation    in   the   visible    spectrum    inhibiting   the 
germination  of  light-sensitive  lettuce  seed.   Smithsonian  Misc.  Coll., 
vol.  94,  no.  5,  pp.  i-ii. 
1936.    The  action  of  radiation  of  specific  wave-lengths   in  relation  to  the 
germination  of   light-sensitive   lettuce   seed.    Compt.   Rend.   Assoc. 
Internat.  Ess.  Sem.,  Copenhagen. 
Johnston,  Earl  S. 
1934.    Phototropic  sensitivity  in  relation  to  wave  length.    Smithsonian  Misc. 
Coll.,  vol.  92,  no.  II,  pp.  1-17. 
KOMMERELL,    E. 
1927.    Quantitative  Versuche   iiber  den   Einfluss  des   Lichtes  verschiedener 
Wellenlangen   auf  die   Keimung   von   Samen.    Jahrb.   Wiss.    Bot., 
vol.  66,  pp.  461-512. 
McNiCHOLAS,  H.  J. 
1931.    The  visible  and  ultra-violet  absorption  spectra  of  carotin  and  xantho- 
phyll   and   the   changes   accompanying   oxidation.     Bur.    Standards 
Journ.  Res.,  vol.  7,  pp.  171-193. 
Meischke,  D. 
1936.    L'eber   den   Einfluss   der   Strahlung   auf   Licht-   und   Dunkel-keimer. 
Jahrb.  Wiss.  Bot.,  vol.  83,  pp.  359-405. 
