﻿Studies 
  of 
  Photo-synthesis 
  in 
  Fresh-water 
  AlgcB. 
  

  

  213 
  

  

  dioxide 
  from 
  sodium 
  bicarbonate 
  lies 
  between 
  1 
  mm. 
  and 
  2 
  mm. 
  of 
  mercury, 
  

   so 
  it 
  is 
  ample 
  to 
  supply 
  the 
  needs 
  of 
  the 
  algse 
  ; 
  also 
  the 
  nitrous 
  system 
  was 
  so 
  

   arranged 
  as 
  to 
  give 
  off 
  the 
  nitrous 
  fumes 
  at 
  such 
  a 
  rate 
  that 
  the 
  algse 
  could 
  

   cope 
  with 
  them 
  and 
  utilise 
  them, 
  so 
  that 
  the 
  nutrient 
  medium 
  did 
  not 
  

   become 
  acid. 
  

  

  Examined 
  on 
  August 
  30 
  {i.e., 
  14 
  days 
  after 
  the 
  addition 
  of 
  the 
  side-tube), 
  

   it 
  is 
  found 
  that 
  Nos. 
  1 
  and 
  2 
  (no 
  addition) 
  and 
  Nos. 
  5 
  and 
  6 
  (nitrites 
  only) 
  

   are 
  dead 
  and 
  degenerating. 
  This 
  had 
  occurred 
  in 
  about 
  a 
  day 
  in 
  Nos. 
  5 
  

   and 
  6, 
  probably 
  because 
  they 
  could 
  not 
  grow 
  from 
  lack 
  of 
  carbon 
  dioxide, 
  

   and 
  so 
  the 
  oxide 
  of 
  nitrogen 
  absorbed 
  by 
  their 
  culture 
  media 
  accumulated 
  

   and 
  killed 
  them. 
  Degeneration 
  did 
  not 
  occur 
  in 
  Nos. 
  1 
  and 
  2 
  for 
  about 
  a 
  

   week 
  to 
  ten 
  days, 
  but 
  at 
  the 
  end 
  of 
  the 
  fortnight 
  they 
  were 
  obviously 
  dead 
  

   and 
  degenerating. 
  

  

  The 
  contrast 
  in 
  the 
  case 
  of 
  the 
  other 
  four 
  jars 
  was 
  striking 
  ; 
  all 
  four 
  had 
  

   lived, 
  increased 
  in 
  amount, 
  and 
  were 
  flourishing 
  at 
  the 
  end. 
  It 
  was 
  obvious 
  

   that 
  the 
  pair 
  which 
  had 
  received 
  both 
  carbon 
  dioxide 
  and 
  oxides 
  of 
  nitrogen 
  

   were 
  much 
  in 
  advance 
  of 
  the 
  other 
  pair, 
  which 
  had 
  been 
  supplied 
  with 
  

   carbon-dioxide 
  only. 
  The 
  latter, 
  of 
  course, 
  had 
  a 
  supply 
  of 
  elemental 
  

   nitrogen 
  in 
  the 
  enclosed 
  air 
  of 
  the 
  jar. 
  

  

  The 
  united 
  contents 
  of 
  each 
  pair 
  of 
  jars, 
  when 
  Kjeldahled, 
  gave 
  the 
  

   following 
  results 
  : 
  — 
  

  

  Nos. 
  7 
  and 
  8 
  (both 
  sod. 
  bicarb, 
  and 
  oxides 
  of 
  nitrogen) 
  14*10 
  „ 
  

  

  The 
  larger 
  weight 
  of 
  nitrogen 
  found 
  in 
  Nos. 
  5 
  and 
  6, 
  which 
  did 
  not 
  grow 
  

   after 
  addition 
  of 
  oxides 
  of 
  nitrogen, 
  as 
  compared 
  with 
  the 
  controls 
  of 
  the 
  

   previous 
  experiment, 
  arises 
  from 
  the 
  growth 
  during 
  the 
  first 
  week 
  open 
  to 
  

   the 
  atmosphere, 
  when 
  the 
  growths 
  were 
  allowed 
  to 
  strike 
  ; 
  no 
  such 
  period 
  was 
  

   allowed 
  in 
  the 
  preceding 
  experiment. 
  If 
  the 
  amount 
  of 
  2 
  50 
  mgrm. 
  in 
  this 
  

   pair 
  be 
  taken 
  as 
  the 
  control, 
  then 
  the 
  amount 
  of 
  nitrogen 
  fixed 
  by 
  jars, 
  with 
  

   no 
  additions, 
  before 
  succumbing 
  to 
  lack 
  of 
  carbon 
  dioxide 
  is 
  - 
  96 
  mgrm. 
  

   When 
  carbon 
  dioxide 
  is 
  supplied 
  from 
  the 
  sodium 
  bicarbonate, 
  but 
  no 
  oxides 
  

   of 
  nitrogen 
  are 
  given 
  to 
  the 
  air, 
  so 
  that 
  the 
  only 
  source 
  for 
  the 
  fixation 
  of 
  

   nitrogen* 
  is 
  the 
  elemental 
  nitrogen 
  of 
  the 
  air 
  enclosed 
  in 
  the 
  jars, 
  this 
  figure 
  

   rises 
  to 
  (5"40 
  — 
  2*50) 
  2'90 
  mgrm. 
  This 
  result 
  is 
  of 
  high 
  importance, 
  for 
  it 
  

  

  * 
  As 
  we 
  have 
  shown 
  in 
  a 
  previous 
  paper, 
  this 
  air 
  contains 
  a 
  trace 
  of 
  nitrites, 
  but 
  

   the 
  amount 
  in 
  the 
  few 
  hundred 
  cubic-centimetres 
  of 
  air 
  contained 
  in 
  the 
  jar 
  is 
  

   infinitesimal 
  and 
  may 
  be 
  neglected. 
  

  

  Nos. 
  1 
  and 
  2 
  (no 
  additions) 
  

  

  Nbs. 
  3 
  and 
  4 
  (sod. 
  bicarb, 
  only) 
  

  

  Nos. 
  5 
  and 
  6 
  (oxides 
  of 
  nitrogen 
  only) 
  

  

  Nitrogen. 
  

   3'46 
  mgrm. 
  

  

  