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  Experimental 
  Researches 
  on 
  Vegetable 
  Assimilation 
  and 
  

   Respiration. 
  XIII.* 
  — 
  The 
  Development 
  of 
  Photosynthetic 
  

   Activity 
  during 
  Germination. 
  

  

  By 
  G. 
  E. 
  Briggs, 
  Demonstrator 
  in 
  Plant 
  Physiology 
  in 
  the 
  University 
  

  

  of 
  Cambridge. 
  

  

  (Communicated 
  by 
  F. 
  F. 
  Blackman, 
  F.R.S. 
  Received 
  March 
  29, 
  1920.) 
  

  

  Introduction. 
  

  

  We 
  must 
  assume 
  that 
  the 
  development 
  of 
  every 
  leaf 
  begins 
  with 
  a 
  stage 
  in 
  

   which 
  it 
  is 
  incapable 
  of 
  performing 
  the 
  function 
  of 
  assimilation. 
  It 
  is 
  a 
  

   matter 
  for 
  investigation 
  to 
  determine 
  whether 
  this 
  stage 
  is 
  passed 
  when 
  the 
  

   tiny 
  leaf 
  first 
  becomes 
  visible 
  in 
  the 
  bud 
  or 
  whether 
  it 
  persists 
  even 
  after 
  the 
  

   leaf 
  is 
  unfolded 
  and 
  fully 
  green. 
  

  

  For 
  seedlings 
  this 
  matter 
  is 
  very 
  important 
  biologically, 
  because 
  it 
  deter- 
  

   mines 
  when 
  the 
  plant 
  can 
  begin 
  to 
  make 
  additions 
  to 
  its 
  dry 
  weight 
  and 
  

   start 
  its 
  natural 
  development. 
  Analysis 
  of 
  results 
  of 
  growth 
  experiments 
  

   on 
  such 
  plants 
  as 
  maize 
  indicates 
  that 
  the 
  early 
  assimilatory 
  power 
  is 
  very 
  

   feeble.f 
  

  

  In 
  most 
  methods 
  of 
  experimenting 
  on 
  the 
  relation 
  of 
  photosynthetic 
  

   activity 
  to 
  the 
  development 
  of 
  chlorophyll-greenness 
  the 
  work 
  is 
  complicated 
  

   by 
  the 
  fact 
  that 
  during 
  the 
  period 
  of 
  illumination 
  of 
  the 
  experiment 
  the 
  

   chlorophyll 
  continues 
  to 
  increase 
  in 
  amount 
  so 
  that 
  one 
  cannot 
  maintain 
  a 
  

   constant 
  greenness 
  for 
  precise 
  investigation. 
  A 
  method 
  of 
  experimentation 
  

   devised 
  by 
  Dr. 
  F. 
  F. 
  Blackman, 
  and 
  used 
  in 
  this 
  laboratory, 
  allows 
  photo- 
  

   synthesis 
  to 
  be 
  measured 
  in 
  an 
  atmosphere 
  with 
  so 
  low 
  an 
  oxygen 
  pressure 
  

   that 
  further 
  chlorophyll 
  development 
  is 
  inhibited, 
  and 
  the 
  green 
  tone 
  can 
  be 
  

   kept 
  constant 
  for 
  days 
  while 
  the 
  leaf 
  is 
  exposed 
  to 
  light. 
  

  

  With 
  this 
  procedure 
  the 
  development 
  of 
  photosynthesis 
  has 
  been 
  followed 
  

   from 
  about 
  zero 
  to 
  nearly 
  full 
  activity. 
  The 
  results, 
  besides 
  throwing 
  light 
  

  

  * 
  Since 
  the 
  publication 
  of 
  Part 
  IX 
  (' 
  Roy. 
  Soc. 
  Proc.,' 
  B, 
  vol. 
  83, 
  p. 
  389) 
  of 
  this 
  series, 
  

   carried 
  out 
  in 
  the 
  Botany 
  School, 
  Cambridge, 
  under 
  the 
  general 
  direction 
  of 
  Dr. 
  F. 
  F. 
  

   Blackman, 
  the 
  following 
  parts 
  have 
  appeared 
  elsewhere 
  : 
  — 
  X. 
  A. 
  A. 
  Irving, 
  " 
  The 
  

   Effect 
  of 
  Chloroform 
  upon 
  Respiration 
  and 
  Assimilation," 
  ' 
  Annals 
  of 
  Botany,' 
  vol. 
  25, 
  

   p. 
  1077 
  (1911). 
  XI. 
  D. 
  Thoday, 
  " 
  On 
  the 
  Effect 
  of 
  Chloroform 
  on 
  the 
  Respiratory 
  

   Exchanges 
  of 
  Leaves," 
  'Annals 
  of 
  Botany,' 
  vol. 
  27, 
  p. 
  697 
  (1913). 
  XII. 
  A. 
  M. 
  Smith, 
  

   "The 
  Temperature-Coefficient 
  of 
  Photosynthesis," 
  'Annals 
  of 
  Botany,' 
  vol. 
  33, 
  p. 
  517 
  

   (1919). 
  

  

  t 
  Briggs, 
  G. 
  E., 
  Kidd, 
  F., 
  and 
  West, 
  C, 
  " 
  Quantitative 
  Analysis 
  of 
  Plant 
  Growth," 
  

   ' 
  Ann. 
  Appl. 
  Biol.,' 
  vol. 
  7, 
  No. 
  1 
  (1920). 
  

  

  