﻿Studies 
  of 
  Photo-synthesis 
  in 
  Fresh-water 
  Algce. 
  209 
  

  

  Commentary. 
  — 
  Several 
  distinct 
  facts 
  are 
  shown 
  by 
  this 
  experiment, 
  and 
  

   taking 
  the 
  final 
  amount 
  of 
  nitrogen 
  as 
  quantitative 
  guide, 
  these 
  will 
  now 
  be 
  

   pointed 
  out. 
  It 
  is 
  interesting 
  in 
  the 
  first 
  place 
  to 
  notice 
  the 
  increase 
  in 
  

   nitrogen 
  which 
  could 
  only 
  come 
  from 
  the 
  atmosphere 
  in 
  those 
  cases 
  where 
  no 
  

   source 
  of 
  nitrogen 
  was 
  added 
  from 
  without, 
  but 
  other 
  essential 
  conditions 
  of 
  

   growth 
  were 
  more 
  or 
  less 
  perfectly 
  satisfied. 
  It 
  is 
  next 
  of 
  importance 
  to 
  note 
  

   the 
  effects 
  of 
  limiting 
  each 
  essential 
  factor 
  in 
  turn, 
  namely, 
  carbon 
  dioxide, 
  

   easily 
  available 
  nitrogen 
  (nitrites), 
  alkaline 
  phosphate, 
  and 
  to 
  note 
  the 
  great 
  

   swing 
  in 
  photo-synthesis 
  in 
  No. 
  7, 
  where 
  all 
  are 
  adequately 
  satisfied. 
  Lastly, 
  

   the 
  important 
  proof 
  is 
  clearly 
  furnished, 
  we 
  believe, 
  for 
  the 
  first 
  time, 
  that 
  

   carbon 
  dioxide 
  can 
  be 
  completely 
  cut 
  off 
  if 
  its 
  place 
  be 
  supplied 
  by 
  simple 
  

   organic 
  substances, 
  such 
  as 
  formaldehyde 
  and 
  inethylic 
  alcohol, 
  which 
  have 
  

   hitherto 
  been 
  regarded 
  as 
  the 
  first 
  products 
  of 
  photo-synthesis 
  in 
  the 
  green 
  

   cell, 
  on 
  purely 
  circumstantial 
  evidence, 
  or 
  upon 
  very 
  weak 
  and 
  uncertain 
  

   positive 
  experiments. 
  

  

  The 
  uptake 
  of 
  nitrogen 
  from 
  the 
  atmosphere 
  is 
  shown 
  by 
  the 
  difference 
  

   between 
  Nos. 
  1 
  and 
  2 
  with 
  nothing 
  whatever 
  added, 
  only 
  tap-water 
  and 
  a 
  

   slight 
  insemination 
  with 
  the 
  algae 
  present, 
  the 
  sole 
  difference 
  being 
  that 
  

   No. 
  1 
  is 
  screwed 
  up 
  airtight, 
  while 
  No. 
  2 
  is 
  open 
  to 
  the 
  air. 
  The 
  difference 
  

   in 
  nitrogen-content, 
  1*6 
  — 
  0'3 
  = 
  1*3 
  mgrm. 
  is 
  quite 
  unmistakable. 
  The 
  

   limiting 
  factor 
  to 
  growth 
  here 
  is 
  unquestionably 
  deficiency 
  in 
  phosphate 
  in 
  

   the 
  tap-water, 
  as 
  is 
  clearly 
  proven 
  by 
  Nos. 
  5 
  and 
  6, 
  where 
  this 
  defect 
  is 
  

   supplied. 
  This 
  experiment 
  again 
  in 
  a 
  still 
  stronger 
  way 
  shows 
  the 
  absorption 
  

   of 
  nitrogen 
  from 
  the 
  air. 
  

  

  The 
  fillip 
  of 
  the 
  phosphate 
  in 
  No. 
  6, 
  with 
  screwed-down 
  lid, 
  has 
  caused 
  

   a 
  light 
  commencing 
  growth 
  until 
  carbon 
  dioxide 
  became 
  exhausted, 
  amounting 
  

   to 
  1 
  mgrm. 
  ; 
  but 
  when 
  this 
  is 
  contrasted 
  with 
  No. 
  5, 
  differing 
  only 
  in 
  access 
  

   of 
  air, 
  i.e., 
  available 
  carbon 
  dioxide 
  and 
  nitrogen, 
  the 
  figure 
  runs 
  up 
  to 
  

   81 
  mgrm., 
  an 
  increase 
  of 
  71 
  mgrm. 
  Now 
  taking 
  this 
  No. 
  5 
  as 
  it 
  stands 
  by 
  

   itself, 
  and 
  not 
  contrasting 
  it 
  with 
  any 
  of 
  the 
  others, 
  the 
  proof 
  is 
  given 
  that 
  

   in 
  200 
  c.c. 
  of 
  tap 
  water, 
  plus 
  2 
  c.c. 
  of 
  5 
  per 
  cent, 
  solution 
  of 
  di-sodium 
  

   hydrogen 
  phophate, 
  plus 
  a 
  minute 
  insemination 
  of 
  Chlorella, 
  there 
  is 
  an 
  

   abundant 
  growth, 
  and 
  the 
  absorption 
  from 
  the 
  air 
  of 
  7 
  to 
  8 
  mgrm. 
  of 
  nitrogen. 
  

   The 
  controls 
  are 
  abundant 
  and 
  the 
  conclusion 
  seems 
  to 
  us 
  inevitable. 
  

  

  Next 
  observe 
  the 
  effects 
  of 
  a 
  luxus 
  addition 
  of 
  easily 
  available 
  nitrogen 
  as 
  

   nitrite, 
  as 
  shown 
  by 
  No. 
  7. 
  This 
  differs 
  from 
  No. 
  5 
  only 
  in 
  the 
  extra 
  addition 
  

   to 
  the 
  culture 
  medium 
  of 
  0"05 
  per 
  cent, 
  of 
  sodium 
  nitrite, 
  and 
  the 
  crop 
  goes 
  

   up 
  by 
  50 
  per 
  cent, 
  from 
  81 
  to 
  12*3 
  mgrm. 
  Similarly 
  in 
  the 
  effect 
  produced 
  

   by 
  manuring 
  with 
  ammonium 
  salts 
  or 
  nitrates, 
  a 
  luxury 
  supply 
  produces 
  a 
  

   luxus 
  crop. 
  

  

  