6  SMITHSONIAN    MISCELLANEOUS    COLLECTIONS  VOL.    96 
mately  i  percent,  but  since  it  is  assumed  that  the  thermocouple-filter 
system  measures  the  light  effective  in  photosynthesis  equally  accu- 
rately in  the  two  cases,  it  is  well  to  bear  in  mind  that  a  greater  photo- 
synthetic  efficiency  may  exist  in  one  light  than  in  the  other.  This  may 
be  the  case  because  of  the  difference  in  color  of  the  light  after  it  passes 
through  the  Polaroid.  Pollard  (1936)  has  noted  the  wave-length  dis- 
tribution characteristics  of  the  Polaroid.  Because  the  light  transmitted 
is  somewhat  different  in  wave-length  distribution  from  the  screened 
Mazda  light,  accurate  comparisons  are  exceedingly  difficult. 
In  summarizing,  it  may  be  concluded  from  the  experimental  evi- 
dence here  presented  that  polarized  light  has  no  effect  other  than 
that  of  ordinary  light  in  phototropism  of  Avena  Markton.  If  there 
is  a  difference  it  is  less  than  the  3  percent  accuracy  of  the  experi- 
mental technique.  Also,  there  is  little  evidence  that  polarized  light 
acts  any  differently  from  nonpolarized  light  of  equal  intensity  and 
similar  wave-length  distribution  in  the  process  of  CO-  assimilation. 
LITERATURE  CITED 
Baly,  E.  C.  C,  and  Semmens,  E.  S. 
1924.    The  selective  photochemical  action  of  polarized  light.   I.  The  hydroly- 
sis of  starch.   Proc.  Roy.  Soc.  London,  ser.  B,  vol.  97,  pp.  25o-25"3. 
Castle,  E.  S. 
1931.  The  phototropic  sensitivity  of  Phycomyces  as  related  to  wave-length. 
Journ.  Gen.  Physiol.,  vol.  14,  pp.  701-71 1. 
Castle,  E.  S. 
1934.  The  phototropic  effect  of  polarized  light.  Journ.  Gen.  Physiol.,  vol.  17, 
pp.  751-762. 
Crozier,  W.  J.,  and  Mangelsdorf,  A.  F. 
1924.    A  note  on  the  relative  photosensory  effect  of  polarized  light.    Journ. 
Gen.  Physiol.,  vol.  6,  no.  6,  pp.  703-706. 
Dastur,  R.  H.,  and  Asana,  R.  D. 
1932.  Effect  of  plane-polarized  light  on  the  formation  of  carbohydrates  in 
leaves.   Ann.  Bot.,  vol.  46,  pp.  879-891. 
Dastur,  R.  H.,  and  Gunjikar,  L.  K. 
1935.  Energy  absorbed  by  leaves  in  normal  and  plane  polarized  light.   Ann. 
Bot.,  vol.  49,  pp.  273-281. 
Du  Buy,  H.  G.,  and  Nuernbergk,  E.  L. 
1935-    Phototropismus  und  Wachstum  den  Pflanzen  (dritter  Teil).    Ergebn. 
Biol.,  vol.  12,  pp.  325-543- 
Garner,  W.  W. 
1937.    Do  the  phases  of  the  moon  affect  plant  growth?     (Mimeographed.) 
Bur.  Plant  Ind.,  U.  S.  Dep.  Agr.,  February. 
Hoover,  W.  H. 
1937-  The  dependence  of  carbon  dioxide  assimilation  in  a  higher  plant  on 
wave  length  of  radiation.  Smithsonian  Misc.  Coll.,  vol.  95,  no.  21, 
pp.  1-13. 
