NO.    6  GROWTH    OF   AVENA    COLEOPTILE JOHNSTON  1 5 
Du  Buy  and  Nuernbergk  (1934)  report  an  experiment  in  which 
monochromatic  light  of  higher  intensity  (170,  later  80  ergs/cmYsec.) 
was  used.  The  mercury  arc  and  incandescent  lamp  with  appropriate 
glass  and  liquid  filters  were  used.  After  six  days  the  following  lengths 
of  first  internodes  and  coleoptiles  are  given : 
Table  6. — Length  of  First  Intcrnodc  and  Colcoptile  in  Monochromatic  Light 
(After  Du  Buy  and  Nuernbergk) 
Wave  length 
First  internode 
A 
(inesocotyl) 
Coleoptile 
Total  length 
3663 
13.5 
39-5 
53-0 
4358 
18.3 
44.3 
62.6 
5461 
19.7 
51.2 
70.9 
6000 
19.6 
46.4 
66.0 
Dark  control 
22.5 
S0.3 
72.8 
At  the  end  of  four  days  the  average  length  of  mesocotyl  under 
each  of  the  five  difl:"erent  treatments  was  given  as  1.5.  Under  the 
four  conditions  of  illumination,  the  coleoptile  varied  in  length  from 
22  in  the  ultraviolet  to  26.6  in  the  red.  The  dark  value  given  for 
the  coleoptile  was  12.5,  approximately  half  that  of  the  exposed  values. 
At  the  end  of  the  third  day  no  growth  of  the  mesocotyl  was  detected. 
By  the  sixth  day  in  these  experiments  the  primary  leaf  had  broken 
tlirough  in  90  to  100  percent  of  the  seedlings.  In  the  Smithsonian 
experiments  the  primary  leaf  was  usually  at  or  near  the  top  of  the 
coleoptile  but  had  never  broken  through  in  the  plants  of  either  the 
exposed  or  the  dark  series.  From  the  above  table  it  will  be  noted  that 
the  first  internode  or  mesocotyl  of  the  dark  control  was  longer  than 
those  of  the  illuminated  seedlings.  The  coleoptile  was  also  longer 
with  one  exception  than  those  of  the  exposed  seedlings.  The  reason 
for  this  disagreement  with  our  experiments  is  not  clear  unless  it 
may  be  due  to  a  difference  in  oat  varieties  used.  In  the  Smithsonian 
experiments  the  coleoptiles  of  the  dark  controls  were  always  shorter 
than  those  of  the  exposed  plants.  This  was  also  true  on  the  fourth 
day  in  the  experiments  of  Du  Buy  and  Nuernbergk.  At  the  end  of 
six  days,  with  the  exception  of  the  group  exposed  to  3663  A,  there 
is  but  little  dift'erence  in  total  length  of  seedlings.  Here  also  the  total 
length  of  their  dark  control  is  slightly  greater  than  those  of  the 
exposed  series. 
Du  Buy  and  Nuernbergk  (1935)  give  two  explanations  as  to  why 
growth  of  the  mesocotyl  is  depressed.  First,  according  to  their  theory, 
protoplasmic  streaming"  is  correlated  with  the  activity  of  growth  regu- 
lators.   Temperatures  above  25°   C.  and  illumination  retard  proto- 
