﻿256 
  Mr. 
  G. 
  E. 
  Briggs. 
  Experimental 
  Researches 
  on 
  

  

  temperature, 
  may 
  cease 
  to 
  be 
  limiting 
  at 
  a 
  higher 
  temperature. 
  Further, 
  a 
  

   factor 
  such 
  as 
  temperature 
  may 
  affect 
  more 
  than 
  one 
  stage 
  of 
  the 
  process. 
  

  

  This 
  analysis 
  of 
  the 
  process 
  into 
  stages 
  emphasises 
  the 
  importance 
  of 
  due 
  

   consideration 
  being 
  given 
  to 
  such 
  conditions 
  as 
  illumination 
  and 
  temperature 
  

   before 
  making 
  the 
  statement 
  that 
  internal 
  factors, 
  such 
  as 
  chlorophyll 
  or 
  

   those 
  of 
  a 
  protoplasmic 
  nature, 
  are 
  limiting. 
  Such 
  considerations 
  are 
  not 
  

   always 
  given. 
  

  

  On 
  the 
  other 
  hand, 
  if, 
  under 
  constant 
  conditions 
  of 
  illumination 
  and 
  

   temperature, 
  assimilation 
  increases 
  without 
  a 
  corresponding 
  increase 
  in 
  an 
  

   internal 
  factor, 
  such 
  as 
  chlorophyll, 
  then 
  that 
  factor 
  is 
  not 
  limiting 
  the 
  rate 
  

   of 
  reaction 
  under 
  these 
  conditions. 
  Such 
  a 
  conclusion 
  has 
  been 
  arrived 
  at 
  

   with 
  regard 
  to 
  chlorophyll 
  as 
  a 
  result 
  of 
  the 
  considerations 
  set 
  forth 
  in 
  

   Section 
  I. 
  

  

  To 
  elucidate 
  further 
  the 
  nature 
  of 
  the 
  limiting 
  factor 
  in 
  the 
  young 
  leaves, 
  

   the 
  effect 
  of 
  reduced 
  illumination 
  on 
  the 
  rate 
  of 
  assimilation 
  was 
  tested. 
  

   This 
  was 
  done 
  on 
  six 
  different 
  dates 
  by 
  increasing 
  the 
  distance 
  of 
  the 
  lamp 
  

   from 
  the 
  chamber 
  from 
  6 
  cm. 
  to 
  12 
  cm. 
  The 
  results 
  are 
  presented 
  in 
  

   Table 
  B. 
  

  

  Table 
  B. 
  — 
  Effect 
  of 
  Seduction 
  of 
  Illumination 
  on 
  Photosynthetic 
  Activity 
  of 
  

   incompletely 
  Greened 
  Young 
  Leaves 
  of 
  Phaseolus- 
  

  

  Expt. 
  No. 
  

  

  Day 
  from 
  

   sowing. 
  

  

  Assimilation 
  in 
  cubic 
  centimetres 
  of 
  oxygen. 
  

  

  i 
  

  

  Lamp 
  at 
  12 
  cm. 
  Lamp 
  at 
  6 
  cm. 
  

  

  Temperature. 
  

  

  Ill 
  

  

  9th 
  

  

  

  

  

  

  

  10th 
  

  

  3 
  3 
  

  

  5-0 
  

  

  12°-13° 
  C. 
  

  

  

  11th 
  

  

  4 
  3 
  

  

  10 
  "4 
  

  

  13°-14 
  -5" 
  C. 
  

  

  IIlA 
  

  

  12th 
  

  

  3 
  9 
  

  

  9-2 
  

  

  14°-15° 
  C. 
  

  

  IV 
  

  

  13th 
  

  

  3-3 
  

  

  6 
  6 
  

  

  12 
  -5-14° 
  C. 
  

  

  

  14th 
  

  

  3 
  7 
  

  

  7-8 
  

  

  12° 
  C. 
  

  

  VI 
  

  

  17th 
  

  

  5-0 
  

  

  12 
  -0 
  

  

  14 
  -5°-lo 
  -5' 
  C. 
  

  

  Leaves 
  nor 
  

  

  mal 
  green. 
  

  

  

  

  

  The 
  exact 
  ratio 
  of 
  the 
  assimilation 
  of 
  the 
  two 
  different 
  light 
  intensities 
  is 
  

   of 
  no 
  great 
  significance 
  for 
  our 
  analysis. 
  It 
  was 
  proved 
  by 
  a 
  number 
  of 
  

   experiments 
  that 
  with 
  fully-greened 
  leaves 
  the 
  temperature, 
  when 
  about 
  

   15° 
  C, 
  was 
  limiting 
  when 
  the 
  lamp 
  was 
  6 
  cm. 
  distant, 
  and 
  consequently 
  the 
  

   assimilation 
  values 
  given 
  for 
  the 
  fully 
  active 
  leaves 
  under 
  these 
  conditions 
  of 
  

   illumination 
  will 
  be 
  dependent 
  upon 
  the 
  temperature 
  when 
  the 
  latter 
  is 
  at 
  or 
  

   below 
  15° 
  C. 
  

  

  