4  SMITHSONIAN    MISCELLANEOUS    COLLECTIONS  VOL.    96 
room  temperature  less  than  29°  C.  for  at  higher  temperatures  the 
Arlington  Fancy  lettuce  seed  used  in  these  experiments  would  not 
germinate,  irrespective  of  the  light  conditions.  On  account  of  the 
narrow  range  of  wave  lengths  represented  by  the  critical  maxima 
obtained,  no  correction  for  relative  energy  was  applied  to  the  graphic 
representation  of  the  data. 
In  the  data  as  given  in  table  i .  it  may  be  noted  that  there  was  a  more 
or  less  progressive  falling  off  in  the  peak  germination  and  that  there 
was  some  variation  between  the  different  series.  Under  the  conditions 
of  the  experiments,  with  continuous  operation  of  the  spectral  and 
superimposed  light  sources,  a  differential  reduction  in  the  efficiencies 
of  the  lights  was  to  be  expected. 
RESULTS 
A  large  number  of  experiments  were  carried  out  incidental  to  the 
attainment  of  the  prescribed  conditions.  Under  conditions  such  that 
an  additional  intensity  of  blue,  when  superimposed  upon  the  spectral 
light,  would  reduce  the  percentage  germination  in  the  compartment 
yielding  100  percent  germination,  the  following  results  in  table  i  were 
obtained : 
In  conjunction  with  the  results  obtained  as  given  in  table  i,  an 
examination  of  the  absorption  spectra  of  lettuce  seed  extract  in  acetone 
was  undertaken.  The  results  of  this  study  are  given  in  plate  i. 
The  foregoing  results  establish  the  critical  wave  lengths  of  the  radia- 
tion promoting  the  germination  of  the  seed  used  in  these  trials  and 
appear  to  indicate  the  nature  of  the  material  responsible  for  the  reac- 
tion.  The  relative  effectiveness  of  radiation  with  wave  lengths  within 
Table  i. — Percentage  germination  of  light -sensitive  lettuce  seed  in  spectral  green 
to  infrared  radiation  mth  superimposed  blue  light. 
Compartment  width  0.4  inch. 
Series 
Percentage 
germination  at  approximate  wave 
of  compartments 
leng1;hs 
at  centei 
4950  5080 
5180 
5300  5440 
5650 
5710 
5850  6000 
6210 
6400 
6700 
7050 
7500    8aoo 
A 
0 
0 
0 
0 
0 
0 
0 
0 
0 
5-9 
27-3 
100. 0 
64.0 
2.1          0 
B 
0 
0 
0 
0 
0 
0 
0 
0 
0 
0 
30.7 
73-3 
77.8 
0             0 
C 
0 
0 
0 
0 
0 
0 
0 
0 
0 
0 
0 
85.2 
14-3 
0              0 
D 
0 
0 
0 
0 
0 
0 
0 
0 
0 
0 
0 
80.0 
0 
0             0 
E 
0 
0 
0 
0 
0 
0 
0 
0 
0 
0 
0 
65.0 
0 
0             0 
Average 
0 
0 
0 
0 
0 
0 
0 
0 
0 
1. 18 
1 1.6 
80.7 
32.03 
0.42      0 
