﻿250 
  Mr. 
  G. 
  E. 
  Briggs. 
  Experimental 
  Researches 
  on 
  

  

  on 
  the 
  nature 
  of 
  the 
  photosynthetic 
  mechanism, 
  explain 
  why 
  Willstatter 
  

   failed 
  to 
  confirm 
  the 
  results 
  obtained 
  by 
  Irving* 
  in 
  this 
  laboratory 
  in 
  1910. 
  

  

  At 
  this 
  point 
  I 
  wish 
  to 
  express 
  my 
  thanks 
  to 
  Dr. 
  F. 
  F. 
  Blackman 
  for 
  

   suggesting 
  the 
  research 
  and 
  for 
  advice 
  and 
  criticism. 
  

  

  SECTION 
  I.— 
  The 
  Relation 
  of 
  Photosynthetic 
  Activity 
  to 
  Age 
  and 
  Chlorophyll 
  

   Development 
  in 
  Young 
  Leaves. 
  

  

  Method 
  and 
  Procedure. 
  — 
  The 
  principle 
  of 
  Dr. 
  Blackman's 
  new 
  method 
  for 
  

   measuring 
  the 
  output 
  of 
  oxygen 
  during 
  photosynthesis 
  is 
  to 
  illuminate 
  the 
  leaf 
  

   in 
  a 
  small 
  closed 
  chamber 
  in 
  an 
  atmosphere 
  of 
  hydrogen 
  with 
  added 
  carbon 
  

   dioxide. 
  The 
  oxygen 
  produced 
  is 
  determined 
  by 
  circulating 
  the 
  atmosphere 
  

   over 
  palladium 
  black, 
  when 
  the 
  oxygen 
  unites 
  with 
  twice 
  its 
  own 
  volume 
  of 
  

   hydrogen. 
  The 
  resulting 
  reduction 
  in 
  gas 
  volume 
  is 
  measured 
  by 
  means 
  of 
  

   a 
  gas 
  burette 
  in 
  connection 
  with 
  the 
  apparatus. 
  As 
  this 
  reduction 
  is 
  three- 
  

   fold 
  that 
  of 
  the 
  oxygen 
  produced, 
  very 
  small 
  amounts 
  of 
  assimilation 
  can 
  be 
  

   accurately 
  measured. 
  The 
  volume 
  of 
  the 
  synthetic 
  water 
  is 
  of 
  course 
  

   negligible. 
  

  

  The 
  illumination 
  was 
  supplied 
  by 
  an 
  ordinary 
  incandescent 
  filament 
  lamp 
  

   of 
  thirty-two 
  candle 
  power, 
  and 
  was 
  varied 
  for 
  certain 
  test 
  experiments 
  by 
  

   changing 
  the 
  distance 
  of 
  the 
  lamp 
  from 
  the 
  chamber. 
  

  

  The 
  percentage 
  of 
  carbon 
  dioxide 
  in 
  the 
  apparatus 
  was 
  about 
  five, 
  and 
  was 
  

   never 
  allowed 
  to 
  become 
  so 
  small 
  as 
  to 
  limit 
  the 
  rate 
  of 
  photosynthesis. 
  

  

  Various 
  materials, 
  including 
  the 
  young 
  buds 
  of 
  the 
  bean 
  ( 
  Vicia 
  Faba), 
  the 
  

   young 
  leaves 
  of 
  the 
  oat 
  (Avena 
  sativa), 
  and 
  of 
  the 
  dwarf 
  French 
  bean 
  

   (Phaseolus 
  vulgaris), 
  were 
  used 
  in 
  the 
  preliminary 
  experiments, 
  but 
  the 
  last- 
  

   mentioned 
  was 
  found 
  to 
  be 
  the 
  most 
  suitable, 
  and 
  was 
  used 
  for 
  the 
  more 
  

   critical 
  experiments 
  ; 
  in 
  Phaseolus 
  the 
  leaf-area 
  did 
  not 
  change 
  during 
  the 
  

   experiments, 
  whilst 
  in 
  the 
  case 
  of 
  the 
  others, 
  slight 
  unfolding 
  of 
  the 
  leaves 
  

   took 
  place. 
  

  

  Prior 
  to 
  sowing, 
  the 
  seeds 
  were 
  soaked 
  for 
  a 
  short 
  time 
  in 
  a 
  small 
  quantity 
  

   of 
  water 
  at 
  the 
  temperature 
  of 
  the 
  laboratory 
  (12°-15 
  c 
  ' 
  C). 
  When 
  the 
  seeds 
  

   were 
  swollen 
  they 
  were 
  sown 
  in 
  soil 
  in 
  pots 
  and 
  germinated 
  in 
  a 
  hot 
  box 
  

   (24°-25° 
  0.) 
  protected 
  from 
  the 
  action 
  of 
  light 
  with 
  a 
  black 
  cloth. 
  For 
  the 
  

   experiments 
  young 
  yellow 
  leaves 
  were 
  cut 
  from 
  these 
  etiolated 
  plants 
  and 
  

   exposed 
  to 
  light 
  until 
  they 
  had 
  acquired 
  the 
  desired 
  tone 
  of 
  greenness. 
  The 
  

   light 
  was 
  usually 
  that 
  of 
  an 
  incandescent 
  filament 
  lamp 
  in 
  a 
  dark 
  room, 
  and 
  

   was 
  of 
  moderate 
  intensity, 
  so 
  that 
  no 
  retardation 
  of 
  greening 
  was 
  caused 
  by 
  

  

  * 
  Irving, 
  A. 
  A., 
  " 
  The 
  Beginning 
  of 
  Photosynthesis 
  and 
  the 
  Development 
  of 
  Chloro- 
  

   phyll," 
  ' 
  Annals 
  of 
  Botany,' 
  vol. 
  24, 
  pp. 
  805-818 
  (1910). 
  

  

  