﻿264 
  Mr. 
  G. 
  E. 
  Briggs. 
  Experimental 
  Researches 
  on 
  

  

  produced 
  is 
  kept 
  extremely 
  low 
  by 
  being 
  quickly 
  removed 
  and 
  estimated 
  by 
  

   a 
  new 
  method 
  due 
  to 
  Dr. 
  F. 
  F. 
  Blackman. 
  

  

  (4) 
  If 
  a 
  leaf 
  is 
  cut 
  from 
  a 
  seedling 
  (Phaseolus) 
  in 
  the 
  dark 
  at 
  an 
  early 
  

   stage 
  and 
  partially 
  greened 
  by 
  exposure 
  to 
  light 
  in 
  air, 
  its 
  photosynthetic 
  

   activity 
  will 
  be 
  very 
  small 
  or 
  nothing, 
  while 
  if 
  exactly 
  the 
  same 
  procedure 
  is 
  

   repeated 
  with 
  a 
  similar 
  leaf 
  from 
  the 
  same 
  plant 
  a 
  few 
  days 
  later, 
  quite 
  strong 
  

   photosynthetic 
  activity 
  will 
  be 
  found. 
  

  

  (5) 
  This 
  alteration 
  of 
  the 
  internal 
  factor 
  with 
  age 
  explains 
  why 
  

   Willstatter 
  has 
  failed 
  to 
  confirm 
  the 
  observations 
  published 
  by 
  Miss 
  Irving 
  

   in 
  1910, 
  proving 
  that 
  young 
  leaves 
  of 
  a 
  full 
  green 
  colour 
  might 
  yet 
  possess 
  

   no 
  power 
  of 
  photosynthesis. 
  Miss 
  Irving 
  used 
  very 
  young 
  leaves, 
  while 
  

   Willstatter 
  happened 
  to 
  use 
  leaves 
  cut 
  from 
  plants 
  some 
  nine 
  days 
  older. 
  In 
  

   the 
  present 
  research 
  the 
  results 
  of 
  both 
  observers 
  have 
  been 
  obtained 
  in 
  

   succession 
  on 
  the 
  same 
  plant. 
  

  

  (6) 
  The 
  conception 
  of 
  the 
  photosynthetic 
  process 
  as 
  consisting 
  of 
  stages 
  

   such 
  as 
  diffusion, 
  photochemical, 
  and 
  chemical 
  stages 
  necessitates 
  the 
  con- 
  

   sideration 
  of 
  external 
  factors 
  when 
  stating 
  that 
  an 
  internal 
  factor 
  is 
  limiting. 
  

  

  (7) 
  Consideration 
  of 
  the 
  results 
  here 
  presented 
  shows 
  that 
  the 
  activity 
  of 
  

   the 
  photochemical 
  part 
  of 
  the 
  photosynthetic 
  mechanism 
  in 
  young 
  seedling 
  

   leaves 
  as 
  compared 
  with 
  that 
  of 
  more 
  mature 
  leaves 
  is 
  in 
  some 
  way 
  limited, 
  

   but 
  apparently 
  the 
  photochemical 
  part 
  depends 
  for 
  its 
  intensity 
  not 
  only 
  upon 
  

   chlorophyll 
  but 
  also 
  upon 
  some 
  other 
  factor. 
  This 
  factor 
  increases 
  with 
  age 
  

   during 
  the 
  early 
  stages 
  of 
  leaf 
  development. 
  

  

  (8) 
  Willstatter's 
  conclusion 
  that 
  chlorophyll 
  was 
  limiting 
  in 
  his 
  results 
  

   with 
  etiolated 
  leaves 
  is 
  based 
  upon 
  insufficient 
  evidence. 
  Full 
  analysis 
  of 
  

   his 
  results 
  with 
  young 
  spring 
  leaves 
  shows 
  that 
  chlorophyll 
  is 
  not 
  limiting, 
  

   just 
  as 
  it 
  is 
  not 
  limiting 
  in 
  Miss 
  Irving's 
  experiments, 
  and 
  in 
  the 
  experiments 
  

   described 
  in 
  the 
  present 
  paper. 
  

  

  Appendix. 
  — 
  Assimilation 
  Experiments. 
  

  

  Each 
  Table 
  refers 
  to 
  the 
  experiment 
  of 
  that 
  number 
  in 
  the 
  text. 
  The 
  first- 
  

   measurement 
  of 
  assimilation 
  was 
  made 
  immediately 
  after 
  greening, 
  except 
  in 
  

   the 
  " 
  A 
  " 
  experiments, 
  when 
  the 
  leaves 
  were 
  kept 
  in 
  the 
  dark 
  during 
  the 
  

   period 
  between 
  the 
  time 
  of 
  greening 
  and 
  measurement 
  of 
  assimilation. 
  

   During 
  the 
  periods 
  between 
  the 
  estimations 
  of 
  assimilation 
  the 
  leaves 
  wer& 
  

   kept 
  in 
  the 
  dark 
  in 
  air 
  at 
  the 
  temperature 
  of 
  the 
  laboratory 
  (14°-15° 
  C. 
  in 
  

   Experiments 
  I- 
  VI) 
  except 
  in 
  Experiment 
  Ia 
  when 
  the 
  temperature 
  was 
  

   24° 
  — 
  25° 
  C. 
  A 
  preliminary 
  of 
  about 
  one 
  hour 
  in 
  the 
  apparatus, 
  prior 
  to- 
  

   estimation 
  of 
  assimilation, 
  was 
  allowed. 
  

  

  