NO.    6  GROWTH    OF    AVENA    COLEOPTILE JOHNSTON  9 
In  order  to  visualize  these  ratio  values,  figure  3  has  been  con- 
structed. The  average  ratio  value  of  first  internode  to  total  length 
per  wave  length  is  indicated  by  the  dash  curve  (L).  The  correspond- 
ing dark  values  are  shown  as  the  continuous  curve  (D).  It  will  be 
noted  that  in  the  exposed  series  there  is  a  fairly  consistent  drop  in 
the  curve  from  about  5000  A  to  the  region  6400-6600  A.  From 
this  region  the  curve  rises  to  a  second  maximum  at  7600  A.  The 
dark  control  curve  shows  much  the  same  shape,  and  this  would  indi- 
cate that  some  stray  light  or  some  common  external  factor  was  affect- 
.00- 
1                                                        1                                                        1 
1 
- 
n  > ^. 
/ 
- 
.80- 
-80" 
-70° 
g     • •...           ..•■         ■•.                               \ 
1    T           -v ^            \                             \ 
/ 
■ 
^ 
y 
^ 
t 
f-  - 
/ 
0 
5 
.60- 
• 
• 
- 
.40- 
1                                       1                                       1 
1 
6000 
tVAI/£   LE/VOTH 
Fig.  3. — Graphs  showing  the  average  ratio  values  of  first  internode  to  total 
seedling  length  per  wave-length  region  of  the  exposed  series  (L)  and  the 
corresponding  average  ratio  values  of  the  dark  series  (D).  The  ratio  values  of 
the  exposed  series  divided  by  the  corresponding  values  of  the  dark  series  are 
plotted  as  curve  R.    T  is  the  average  temperature  curve. 
ing  the  growth  of  the  first  internode.  If  it  be  assumed  that  all 
external  growth  conditions  be  the  same  in  the  two  series  with  the 
exception  of  light,  then  the  effect  of  light  is  shown  by  dividing  the 
values  of  the  exposed  series  by  those  of  the  dark  series.  The  values 
in  column  7  of  table  2  have  therefore  been  plotted  in  figure  3  as  the 
dash-dot  curve  (R).  This  curve  shows  a  distinct  falling  off  in  the 
region  6400-6600  A,  with  two  maximal  regions  4800-5000  A  and 
7600  A. 
Since  it  is  probable  that  there  were  some  scattered  light  effects  in 
all  but  the  first  nine  experiments  of  the  dark  series,  curve  L  probably 
gives  a  better  idea  of  the  light  response  of  the  first  internode  as 
