﻿260 
  Mr. 
  G. 
  E. 
  Briggs. 
  Experimental 
  Researches 
  on 
  

  

  chlorophyll-content, 
  would 
  be 
  a 
  nearer 
  indication 
  of 
  chlorophyll 
  being- 
  

   limiting. 
  In 
  no 
  way 
  can 
  it 
  be 
  said 
  that 
  Willstatter's 
  results 
  prove 
  

   chlorophyll 
  to 
  be 
  limiting 
  in 
  the 
  early 
  stages. 
  The 
  increase 
  in 
  assimilation,, 
  

   with 
  increase 
  in 
  chlorophyll-content 
  observed, 
  may 
  be 
  due 
  to 
  increase 
  in 
  

   other 
  internal 
  factors 
  uncontrolled 
  and 
  not 
  brought 
  into 
  account. 
  This 
  

   point 
  will 
  be 
  taken 
  up 
  again 
  later. 
  

  

  To 
  return 
  to 
  Irving's 
  experiments, 
  and 
  the 
  suggestion 
  that 
  here 
  light 
  was 
  

   the 
  factor 
  limiting 
  the 
  assimilation, 
  there 
  would 
  appear 
  to 
  be 
  no 
  grounds 
  for 
  

   this 
  suggestion. 
  J0rgensen 
  and 
  Stiles 
  state 
  that 
  Irving 
  exposed 
  her 
  plants 
  

   to 
  the 
  feeble 
  light 
  of 
  a 
  north 
  window. 
  Reference 
  to 
  her 
  paper, 
  however, 
  

   will 
  show 
  that 
  such 
  was 
  the 
  case 
  in 
  her 
  two 
  preliminary 
  experiments, 
  but 
  

   .that 
  in 
  her 
  critical 
  ones 
  she 
  used 
  two 
  Keith 
  high-pressure 
  burners. 
  Further, 
  

   since 
  she 
  obtained 
  the 
  same 
  results 
  with 
  feeble 
  light 
  as 
  with 
  strong 
  light 
  

   with 
  leaves 
  which 
  had 
  developed 
  an 
  almost 
  normal 
  amount 
  of 
  chlorophyll, 
  it 
  

   may 
  be 
  concluded 
  that 
  the 
  intensity 
  of 
  illumination 
  had 
  no 
  great 
  effect 
  on 
  

   the 
  results. 
  

  

  There 
  still 
  remains 
  the 
  task 
  of 
  explaining 
  the 
  difference 
  between 
  the 
  

   results 
  obtained 
  by 
  Irving 
  and 
  by 
  Willstatter 
  under 
  similar 
  conditions. 
  

   At 
  first, 
  it 
  seemed 
  possible 
  that 
  the 
  difference 
  might 
  be 
  due 
  to 
  the 
  fact 
  that,, 
  

   except 
  iu 
  her 
  first 
  experiment, 
  Irving's 
  leaves 
  greened 
  after 
  being 
  cut 
  from 
  

   the 
  plant, 
  and 
  that 
  they 
  greened 
  in 
  an 
  atmosphere 
  where 
  the 
  carbon 
  

   dioxide 
  was 
  removed 
  as 
  soon 
  as 
  formed. 
  A 
  comparison 
  of 
  leaves, 
  which 
  had 
  

   developed 
  their 
  chlorophyll 
  while 
  attached 
  to 
  the 
  plant 
  and 
  in 
  ordinary 
  air, 
  

   with 
  those 
  which 
  were 
  cut 
  and 
  exposed 
  to 
  light 
  in 
  an 
  atmosphere 
  deprived 
  of 
  

   carbon 
  dioxide, 
  showed 
  that 
  there 
  was 
  no 
  essential 
  difference 
  between 
  their 
  

   rates 
  of 
  assimilation. 
  

  

  In 
  Willstatter's 
  earlier 
  account 
  of 
  his 
  work 
  he 
  gave 
  no 
  record 
  of 
  the 
  

   history 
  of 
  his 
  leaves, 
  but 
  in 
  his 
  1918 
  publication 
  he 
  states 
  that 
  his 
  experi- 
  

   ment, 
  which 
  was 
  done 
  under 
  similar 
  conditions 
  to 
  those 
  of 
  Irving, 
  was 
  

   performed 
  with 
  Phaseolus 
  leaves 
  which 
  were 
  exposed 
  for 
  six 
  hours 
  on 
  the 
  

   14th 
  day 
  from 
  sowing, 
  when 
  the 
  shoots 
  were 
  about 
  12 
  inches 
  high, 
  and 
  

   that 
  the 
  assimilation 
  was 
  measured 
  on 
  the 
  following 
  day. 
  Irving's 
  material, 
  

   however, 
  was 
  taken 
  when 
  the 
  shoots 
  were 
  only 
  4 
  to 
  5 
  inches 
  long, 
  that 
  is 
  r 
  

   five 
  or 
  six 
  days 
  from 
  sowing. 
  Further, 
  Irving 
  measured 
  the 
  assimilation 
  

   directly 
  as 
  the 
  leaves 
  greened 
  ; 
  not 
  24 
  hours 
  afterwards. 
  The 
  writer's 
  

   experiments 
  show 
  that 
  age 
  and 
  lapse 
  of 
  time 
  after 
  greening 
  are, 
  however, 
  

   just 
  the 
  most 
  important 
  factors, 
  and, 
  consequently, 
  it 
  seems 
  safe 
  to 
  conclude 
  

   that 
  the 
  discrepant 
  results 
  are 
  due 
  simply 
  to 
  this, 
  that 
  Irving 
  worked 
  with 
  

   very 
  young 
  leaves 
  while 
  Willstatter 
  used 
  distinctly 
  older 
  material. 
  The 
  

   experiments 
  recorded 
  in 
  this 
  paper 
  pass 
  from 
  the 
  early 
  phase 
  where 
  there 
  is 
  

  

  