﻿238 
  ANNUAL 
  REPORT 
  SMITHSONIAN 
  INSTITUTION, 
  19 
  2 
  9 
  

  

  and 
  it 
  is 
  to 
  these 
  that 
  the 
  color 
  of 
  the 
  leaves 
  is 
  due. 
  The 
  mystery 
  

   of 
  it 
  all 
  lay 
  in 
  the 
  fact 
  that 
  no 
  one 
  knew 
  what 
  actually 
  takes 
  place, 
  

   and, 
  indeed, 
  the 
  more 
  chemists 
  and 
  botanists 
  explored, 
  the 
  more 
  

   puzzling 
  did 
  the 
  problem 
  seem 
  to 
  be. 
  

  

  Perhaps 
  the 
  most 
  puzzling 
  fact 
  of 
  all 
  is 
  that 
  the 
  plant 
  only 
  makes 
  

   use 
  of 
  sunlight, 
  when 
  all 
  our 
  previous 
  knowledge 
  of 
  light 
  reactions 
  

   leads 
  us 
  to 
  believe 
  that 
  such 
  light 
  is 
  quite 
  incapable 
  of 
  inducing 
  

   photosynthesis. 
  This 
  may 
  readily 
  be 
  understood 
  if 
  the 
  amount 
  of 
  

   energy 
  involved 
  in 
  the 
  synthesis 
  is 
  considered. 
  It 
  has 
  been 
  proved 
  

   experimentally 
  that 
  in 
  order 
  to 
  synthesize 
  1 
  gram 
  molecule 
  (180 
  

   grams) 
  of 
  glucose 
  or 
  fructose 
  there 
  must 
  be 
  supplied 
  to 
  the 
  carbonic 
  

   acid 
  a 
  minimum 
  quantity 
  of 
  energy 
  equal 
  to 
  673,800 
  'calories. 
  

   While 
  it 
  is 
  loiown 
  that 
  the 
  plant 
  manages 
  in 
  some 
  way 
  to 
  absorb 
  

   the 
  necessary 
  energy 
  in 
  the 
  form 
  of 
  light, 
  the 
  physicist 
  tells 
  us 
  that 
  

   it 
  can 
  not 
  directly 
  absorb 
  enough 
  energy 
  from 
  sunlight. 
  Thus 
  the 
  

   photosynthesis 
  can 
  be 
  brought 
  about 
  by 
  red 
  light 
  of 
  the 
  wave 
  length 
  

   660mm 
  when 
  the 
  energy 
  directly 
  absorbed 
  can 
  only 
  be 
  260,000 
  calories 
  

   which 
  is 
  far 
  below 
  the 
  minimum 
  quantity 
  required. 
  

  

  The 
  experience 
  gained 
  from 
  the 
  ordinary 
  reactions 
  of 
  photo- 
  

   chemistry 
  leads 
  to 
  the 
  belief 
  that 
  if 
  it 
  is 
  required 
  to 
  convert 
  carbonic 
  

   acid 
  into 
  sugars 
  by 
  means 
  of 
  light 
  alone, 
  it 
  will 
  be 
  necessary 
  to 
  use 
  

   ultra-violet 
  light 
  which 
  is 
  absorbed 
  by 
  carbonic 
  acid, 
  that 
  is 
  to 
  say, 
  

   light 
  of 
  wave 
  length 
  210mm- 
  It 
  is 
  obvious 
  from 
  this 
  that 
  some 
  un- 
  

   known 
  factor 
  is 
  operating 
  in 
  vital 
  photosynthesis. 
  

  

  In 
  any 
  endeavor 
  to 
  elucidate 
  the 
  mystery, 
  it 
  is 
  evident 
  that 
  the 
  

   first 
  line 
  of 
  inquiry 
  must 
  be 
  to 
  study 
  the 
  action 
  of 
  the 
  short 
  wave 
  

   ultra-violet 
  light 
  upon 
  carbonic 
  acid. 
  This 
  was 
  first 
  investigated 
  by 
  

   Moore 
  and 
  Webster 
  in 
  1913, 
  who 
  found 
  no 
  evidence 
  of 
  any 
  reaction 
  

   taking 
  place. 
  They 
  found, 
  however, 
  that 
  in 
  the 
  presence 
  of 
  cer- 
  

   tain 
  catalysts, 
  such 
  as 
  colloidal 
  iron 
  hydroxide, 
  small 
  quantities 
  of 
  

   formaldehyde 
  were 
  produced. 
  Since 
  these 
  results 
  appeared 
  to 
  be 
  at 
  

   variance 
  with 
  general 
  experience 
  in 
  photochemical 
  investigations, 
  

   they 
  were 
  again 
  examined 
  some 
  years 
  later 
  in 
  Liverpool, 
  and 
  it 
  was 
  

   then 
  found 
  that 
  when 
  a 
  stream 
  of 
  carbon 
  dioxide 
  was 
  passed 
  through 
  

   water 
  irradiated 
  by 
  the 
  light 
  from 
  a 
  quartz 
  mercury 
  lamp, 
  small 
  

   quantities 
  of 
  formaldehyde 
  were 
  produced. 
  This 
  result 
  seemed 
  to 
  be 
  

   very 
  satisfactory, 
  since 
  the 
  formaldehyde 
  could 
  be 
  looked 
  upon 
  as 
  an 
  

   intermediate 
  stage 
  on 
  the 
  way 
  to 
  carbohydrates, 
  especially 
  in 
  view 
  of 
  

   the 
  fact 
  that 
  Moore 
  and 
  Webster 
  had 
  proved 
  that 
  formaldehyde 
  was 
  

   converted 
  by 
  light 
  into 
  substance, 
  with 
  properties 
  similar 
  to 
  the 
  

   simple 
  sugars. 
  

  

  Our 
  observations 
  were 
  criticized 
  by 
  Porter 
  and 
  Kamsperger, 
  who 
  

   stated 
  that 
  if 
  rigid 
  precautions 
  were 
  taken 
  to 
  guard 
  against 
  the 
  pres- 
  

   ence 
  of 
  every 
  trace 
  of 
  impurity, 
  no 
  formaldehyde 
  was 
  produced. 
  The 
  

   suggestion 
  was 
  implied 
  by 
  them 
  that 
  the 
  origin 
  of 
  the 
  formaldehyde 
  

  

  