﻿Vegetable 
  Assimilation 
  and 
  Respiration. 
  

  

  257 
  

  

  If 
  the 
  assumption 
  that 
  the 
  " 
  internal 
  " 
  factor 
  which 
  is 
  limiting 
  the 
  photo- 
  

   synthetic 
  process 
  in 
  the 
  early 
  stages 
  is 
  purely 
  of 
  a 
  protoplasmic 
  nature, 
  that 
  

   is, 
  one 
  involved 
  in 
  the 
  chemical 
  or 
  dark 
  stage 
  of 
  the 
  process, 
  be 
  correct, 
  then 
  

   as 
  the 
  following 
  consideration 
  shows, 
  reduction 
  of 
  illumination 
  should 
  not 
  

   have 
  the 
  effect 
  observed. 
  

  

  The 
  maximum 
  value 
  of 
  the 
  assimilation 
  for 
  the 
  fully-greened 
  leaves, 
  with 
  

   the 
  lamp 
  12 
  cm. 
  distant, 
  is 
  5. 
  The 
  assimilation 
  is 
  limited 
  to 
  this 
  value 
  in 
  

   this 
  case 
  by 
  light, 
  that 
  is, 
  by 
  the 
  photochemical 
  stage, 
  since 
  an 
  increase 
  of 
  the 
  

   intensity 
  of 
  illumination 
  leads 
  to 
  an 
  increase 
  in 
  assimilation. 
  If 
  the 
  

   assimilation 
  in 
  the 
  early 
  stages 
  of 
  the 
  young 
  leaves 
  were 
  limited 
  by 
  a 
  

   " 
  protoplasmic 
  " 
  factor 
  only, 
  then 
  whenever 
  this 
  factor 
  determined 
  the 
  

   assimilation 
  of 
  five 
  or 
  more 
  units 
  when 
  the 
  lamp 
  was 
  6 
  cm. 
  distant, 
  the 
  

   assimilation 
  should 
  not 
  be 
  reduced 
  below 
  the 
  value 
  of 
  five 
  when 
  the 
  lamp 
  is 
  

   removed 
  to 
  12 
  cm., 
  since 
  the 
  photochemical 
  part 
  of 
  the 
  mechanism 
  is 
  

   assumed 
  to 
  allow 
  of 
  this 
  value. 
  As 
  this 
  is 
  not 
  the 
  case, 
  the 
  internal 
  limiting 
  

   factor, 
  which 
  determines 
  the 
  assimilation 
  in 
  the 
  early 
  stages 
  of 
  the 
  young- 
  

   leaves 
  when 
  the 
  lamp 
  is 
  12 
  cm. 
  distant, 
  must 
  be 
  concerned 
  with 
  the 
  photo- 
  

   chemical 
  part 
  of 
  the 
  mechanism. 
  

  

  To 
  consider 
  the 
  question 
  from 
  another 
  point 
  of 
  view, 
  in 
  all 
  cases 
  with 
  the 
  

   lamp 
  12 
  cm. 
  distant 
  the 
  assimilation 
  is 
  limited 
  by 
  the 
  photochemical 
  stage, 
  

   since 
  an 
  increase 
  in 
  the 
  intensity 
  of 
  illumination 
  results 
  in 
  an 
  increase 
  of 
  

   assimilation, 
  and 
  consequently 
  as 
  the 
  earlier 
  stages 
  give 
  a 
  smaller 
  value 
  than 
  

   that 
  given 
  by 
  the 
  fully 
  active 
  leaves 
  under 
  the 
  same 
  conditions 
  of 
  illumina- 
  

   tion, 
  we 
  must 
  conclude 
  that 
  this 
  smaller 
  value 
  is 
  to 
  be 
  attributed 
  to 
  an 
  

   internal 
  factor 
  concerned 
  with 
  the 
  photochemical 
  part 
  of 
  the 
  photosynthetic 
  

   mechanism. 
  This 
  limiting 
  factor 
  increases 
  its 
  potentialities 
  from 
  day 
  to 
  day, 
  

   as 
  shown 
  by 
  the 
  increasing 
  values 
  of 
  the 
  assimilation 
  when 
  the 
  lamp 
  is 
  

   maintained 
  at 
  12 
  cm. 
  

  

  The 
  question 
  as 
  to 
  whether 
  the 
  smaller 
  values 
  of 
  assimilation 
  in 
  the 
  earlier 
  

   stages 
  under 
  the 
  conditions 
  of 
  higher 
  illumination 
  were 
  due 
  to 
  this 
  same 
  

   limiting 
  factor 
  could 
  have 
  been 
  decided 
  by 
  testing 
  whether 
  these 
  smaller 
  

   values 
  could 
  have 
  been 
  increased 
  by 
  increasing 
  the 
  intensity 
  of 
  the 
  illumina- 
  

   tion 
  still 
  further. 
  Had 
  the 
  limiting 
  factor 
  been 
  purely 
  of 
  a 
  photochemical 
  

   nature 
  the 
  assimilation 
  would 
  have 
  increased 
  with 
  increasing 
  intensity 
  of 
  

   illumination 
  until 
  the 
  maximum 
  of 
  about 
  12 
  units, 
  determined 
  by 
  the 
  

   chemical 
  stage, 
  had 
  been 
  reached. 
  The 
  light 
  intensity 
  at 
  our 
  disposal 
  was 
  

   not 
  sufficiently 
  great 
  to 
  decide 
  this 
  question. 
  

  

  Speculation 
  as 
  to 
  the 
  nature 
  of 
  this 
  factor 
  is 
  very 
  attractive, 
  but 
  before 
  it 
  

   can 
  be 
  done 
  with 
  advantage 
  more 
  knowledge 
  is 
  required. 
  With 
  certainty 
  it 
  

   can 
  be 
  said 
  that, 
  although 
  it 
  is 
  involved 
  in 
  the 
  photochemical 
  stage, 
  it 
  is 
  not 
  

  

  x 
  2 
  

  

  