﻿258 
  Mr. 
  G. 
  E. 
  Briggs. 
  Experimental 
  Researches 
  on 
  

  

  chlorophyll 
  alone, 
  since 
  it 
  increases 
  in 
  value 
  without 
  increase 
  in 
  chlorophyll- 
  

   content.* 
  Further, 
  the 
  degree 
  of 
  development 
  of 
  this 
  factor 
  is 
  primarily 
  

   dependent 
  upon 
  age 
  and 
  time 
  after 
  greening, 
  as 
  shown 
  in 
  Section 
  I. 
  

   Consequently 
  the 
  indications 
  seem 
  to 
  be 
  that 
  this 
  factor 
  depends 
  upon 
  : 
  

   (1) 
  chlorophyll, 
  since 
  without 
  chlorophyll 
  the 
  photochemical 
  part 
  of 
  the 
  

   photosynthetic 
  mechanism 
  is 
  absent, 
  or 
  practically 
  so 
  ; 
  (2) 
  some 
  other 
  

   factor, 
  working 
  in 
  correlation 
  with 
  chlorophyll, 
  which 
  factor 
  is 
  dependent 
  

   upon 
  age, 
  as 
  very 
  young 
  leaves, 
  no 
  matter 
  what 
  their 
  chlorophyll-content, 
  

   cannot 
  function 
  as 
  assimilating 
  organs 
  (see 
  Table 
  VII 
  in 
  Appendix). 
  Further 
  

   evidence 
  as 
  to 
  its 
  nature 
  is 
  not 
  sufficiently 
  definite 
  to 
  warrant 
  more 
  

   discussion. 
  

  

  Section 
  III. 
  — 
  A 
  Consideration 
  of 
  the 
  Results 
  obtained 
  by 
  Irving 
  and 
  by 
  

   Willstatter 
  on 
  the 
  Relation 
  of 
  Greening 
  to 
  Photosynthesis, 
  and 
  an 
  

   Explanation 
  of 
  the 
  Apparent 
  Contradiction. 
  

  

  Irving, 
  in 
  1910, 
  working 
  with 
  F. 
  F. 
  Blackman, 
  came 
  to 
  the 
  conclusion 
  

   that 
  the 
  development 
  of 
  photosynthetic 
  activity 
  in 
  the 
  young 
  leaves 
  of 
  

   seedlings 
  lagged 
  behind 
  greening. 
  In 
  other 
  words, 
  as 
  the 
  present 
  writer's 
  

   experiments 
  show, 
  the 
  development 
  of 
  photosynthetic 
  activity 
  is 
  dependent 
  

   upon 
  some 
  factor 
  other 
  than 
  chlorophyll. 
  Irving's 
  experiments 
  were 
  

   carried 
  out 
  with 
  a 
  small 
  carbon 
  dioxide 
  supply, 
  namely, 
  that 
  of 
  respiration. 
  

   She 
  found 
  that, 
  under 
  these 
  conditions, 
  the 
  young 
  leaves 
  were 
  unable 
  to 
  reduce 
  

   measurably 
  their 
  carbon 
  dioxide 
  output 
  until 
  after 
  they 
  had 
  reached 
  an 
  

   advanced 
  stage 
  of 
  greening. 
  The 
  illumination 
  used 
  was 
  greater 
  than 
  that 
  

   required 
  hy 
  normal 
  leaves 
  to 
  utilise 
  the 
  whole 
  of 
  their 
  respiratory 
  carbon 
  

   dioxide. 
  

  

  Willstatter 
  and 
  Stoll.f 
  in 
  1915 
  working 
  under 
  what 
  appeared 
  to 
  be 
  

   similar 
  conditions, 
  found 
  that 
  leaves, 
  which 
  had 
  developed 
  only 
  a 
  very 
  

   small 
  portion 
  of 
  their 
  normal 
  chlorophyll-content, 
  were 
  able 
  to 
  utilise 
  for 
  

   assimilation 
  the 
  whole 
  of 
  their 
  respiratory 
  carbon 
  dioxide. 
  This 
  result 
  being 
  

   in 
  direct 
  contradiction 
  to 
  that 
  obtained 
  by 
  Irving, 
  they 
  sought, 
  without 
  

   success, 
  for 
  some 
  explanation. 
  

  

  The 
  only 
  difference 
  of 
  procedure 
  which 
  they 
  consider 
  is, 
  that 
  in 
  their 
  

   experiments 
  they 
  took 
  the 
  temperature 
  of 
  the 
  leaves, 
  and 
  thus 
  were 
  able 
  to 
  

   avoid 
  an 
  increased 
  leaf-temperature 
  on 
  illumination, 
  whilst 
  Irving 
  took 
  the 
  

  

  * 
  Tt 
  may 
  be 
  as 
  well 
  to 
  note 
  that 
  there 
  is 
  no 
  definite 
  evidence 
  as 
  to 
  the 
  nature 
  of 
  the 
  

   green 
  pigment 
  in 
  young 
  leaves, 
  as 
  Willstatter's 
  measurements 
  of 
  chlorophyll 
  are 
  colori- 
  

   metric 
  not 
  chemical, 
  whilst 
  other 
  writers 
  refer 
  to 
  such 
  substances 
  as 
  proto-chlorophyll. 
  

   In 
  this 
  paper 
  the 
  term 
  chlorophyll 
  is 
  used 
  for 
  the 
  green 
  pigment, 
  whatever 
  its 
  nature. 
  

  

  t 
  Willstatter, 
  E,., 
  and 
  Stoll, 
  A., 
  " 
  Untersuchungen 
  iiber 
  die 
  Assimilation 
  der 
  

   Kohlensaure," 
  ' 
  Ber. 
  Deut. 
  Chem. 
  Ges.,' 
  vol. 
  48, 
  pp. 
  1540-1564 
  (1915). 
  

  

  