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SMITHSONIAN    MISCELLANEOUS    COLLECTIONS  VOL.    96 
related  to  total  length  of  seedling  than  curve  R.  It  is  doubtful  if 
temperature  differences  were  great  enough  to  bring  about  marked 
variations  in  growth  rates.  The  average  temperatures  for  each  wave- 
length group  are  plotted  as  the  dotted  curve  (T)  in  figure  3. 
The  average  ratios  of  coleoptile  to  total  length  of  seedlings  are 
not  given  in  table  2,  but  they  may  easily  be  obtained  by  subtracting 
the  values  in  the  third  column  from  i.oo.    The  shape  of  the  curve 
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ty/tt/e     LENGTH 
Fig.  4. — Graph  showing  percentage  of  coleoptile  to  total  length  of  seedling  of 
exposed  series  (continuous  curve).  For  comparison  the  germination  curve 
(dash-dot)  of  light-sensitive  lettuce  seed  (from  Flint  and  McAHster)  and  the 
inverted  phototropic  sensitivity  curve  (dash)  of  Avcna  (from  Johnston)  are 
plotted  in  the  same  figure. 
is  that  of  the  mirror  image  of  curve  L  in  figure  3.  This  smoothed 
coleoptile  curve  has  been  plotted  in  figure  4  as  a  continuous  line.  It 
will  be  observed  that  from  wave  length  4050  A  to  5500  A  the  ratio 
values  are  less  than  0.50.  In  this  region  the  coleoptile  is  less  than 
50  percent  of  the  total  seedling  length.  Furthermore,  the  length  of 
coleoptile  is  greater  than  50  percent  of  the  seedling  length  from  about 
wave  length  5500  A  to  wave  length  7200  A.  Maximum  coleoptile 
elongation  occurs  at  the  region  6400  A  to  6600  A  with  a  minimum 
at  about  4800  A  to  5000  A  and  another  in  the  region  of  7600  A. 
