﻿RELATION 
  OF 
  AQUATIC 
  PLANTS 
  TO 
  SUBSTRATUM. 
  489 
  

  

  deca}^, 
  the 
  substances 
  that 
  the}^ 
  have 
  drawn 
  from 
  the 
  soil 
  come 
  into 
  

   sohition 
  in 
  the 
  water 
  and 
  there 
  add 
  to 
  the 
  supply 
  of 
  food 
  available 
  for 
  

   the 
  phyto-plankton. 
  In 
  thus 
  transferring 
  food 
  materials 
  from 
  the 
  

   soil 
  to 
  the 
  water 
  these 
  plants 
  would 
  serve 
  a 
  most 
  important 
  function, 
  

   analogous 
  to 
  the 
  fertilization 
  of 
  land. 
  

  

  According- 
  to 
  the 
  usual 
  view, 
  the 
  larger 
  aquatics 
  in 
  their 
  aeration 
  

   and 
  mechanical 
  roles 
  tend 
  to 
  increase 
  the 
  supply 
  of 
  tish, 
  while 
  in 
  their 
  

   nutritive 
  role 
  they 
  tend 
  during 
  the 
  growing 
  season 
  to 
  diminish 
  it, 
  

   though 
  on 
  the 
  average 
  not 
  affecting 
  it. 
  From 
  the 
  alternative 
  view, 
  

   they 
  tend 
  in 
  all 
  roles 
  to 
  increase 
  the 
  supply 
  of 
  hsh. 
  It 
  thus 
  becomes 
  

   important 
  to 
  determine 
  the 
  source 
  of 
  nutrition 
  of 
  the 
  larger 
  attached 
  

   aquatic 
  plants. 
  

  

  HISTORICAL 
  REVIEW. 
  

  

  Unger 
  (1861) 
  was 
  probably 
  the 
  tirst 
  to 
  suggest 
  the 
  absorption 
  and 
  

   excretion 
  of 
  water 
  in 
  submerged 
  aquatics. 
  The 
  existence 
  of 
  amphib- 
  

   ious 
  species 
  and 
  those 
  subject 
  to 
  sudden 
  inundation 
  did 
  not 
  escape 
  his 
  

   notice. 
  It 
  seemed 
  unreasonable 
  to 
  him 
  to 
  suppose 
  that 
  the 
  leaves 
  of 
  

   amphibious 
  plants, 
  when 
  exposed, 
  should 
  act 
  as 
  organs 
  of 
  transpira- 
  

   tion, 
  and, 
  when 
  suddenly 
  submerged, 
  as 
  organs 
  of 
  absorption. 
  He 
  

   preferred 
  to 
  think 
  that 
  there 
  is 
  an 
  upward 
  current 
  in 
  water 
  plants 
  as 
  

   well 
  as 
  in 
  land 
  plants, 
  and 
  he 
  endeavored 
  to 
  show 
  that 
  there 
  is 
  a 
  meas- 
  

   urable 
  excretion 
  of 
  water 
  by 
  the 
  leaves. 
  He 
  experimented 
  as 
  follows: 
  

   Two 
  jars 
  filled 
  with 
  water 
  were 
  placed 
  side 
  by 
  side 
  and 
  a 
  U-tube 
  hung 
  

   on 
  the 
  adjacent 
  edges, 
  so 
  that 
  one 
  shank 
  of 
  the 
  tube 
  descended 
  into 
  

   each 
  jar. 
  Plants 
  of 
  Potamogeton 
  crispus 
  were 
  so 
  arranged 
  that 
  their 
  

   roots 
  were 
  in 
  one 
  jar, 
  while 
  the 
  stems, 
  passing 
  through 
  the 
  U-tube, 
  

   were 
  in 
  the 
  other 
  jar. 
  The 
  total 
  leaf 
  surface 
  of 
  the 
  plants 
  was 
  126 
  

   quadricentimeters 
  and 
  they 
  bore 
  7 
  adventitious 
  roots 
  several 
  inches 
  

   long. 
  A 
  preparation 
  similar 
  to 
  the 
  preceding, 
  except 
  that 
  the 
  roots 
  

   were 
  removed, 
  served 
  for 
  a 
  control. 
  At 
  the 
  end 
  of 
  a 
  week 
  the 
  volume 
  

   of 
  water 
  in 
  the 
  jars 
  containing 
  the 
  stem 
  portions 
  had 
  in 
  the 
  tirst- 
  

   mentioned 
  case 
  increased 
  1.6 
  grams, 
  and 
  in 
  the 
  control 
  none 
  whatever. 
  

   Unger 
  obtained 
  a 
  similar 
  result 
  with 
  Ranuncuhis 
  jluitans. 
  

  

  These 
  experiments 
  were 
  not 
  accepted 
  by 
  Strasburger 
  (1891) 
  and 
  

   Hochreutiner 
  (1896), 
  although 
  neither 
  of 
  these 
  men 
  makes 
  specific 
  

   objection. 
  The 
  best 
  reason 
  for 
  not 
  accepting 
  Unger's 
  results 
  is 
  that 
  

   he 
  fails 
  to 
  show 
  that 
  his 
  method 
  of 
  measurement 
  was 
  sufficiently 
  accu- 
  

   rate. 
  An 
  increase 
  of 
  1.6 
  grams 
  is 
  a 
  rather 
  small 
  amount, 
  and 
  unless 
  

   we 
  know 
  that 
  the 
  experimental 
  error 
  must 
  have 
  been 
  less 
  than 
  this 
  

   the 
  result 
  is 
  to 
  be 
  questioned. 
  

  

  Schenck 
  (1886) 
  states 
  that 
  the 
  roots 
  are 
  primarily 
  organs 
  of 
  attach- 
  

   ment, 
  arguing 
  that 
  this 
  must 
  be 
  true 
  since 
  the 
  necessary 
  amount 
  of 
  

   mineral 
  salts 
  is 
  absorbed 
  directly 
  through 
  the 
  epidermis. 
  This 
  is 
  

   purely 
  an 
  assumption 
  on 
  the 
  part 
  of 
  Schenck, 
  as 
  there 
  is 
  no 
  experi- 
  

   mental 
  evidence 
  to 
  support 
  the 
  view.. 
  

  

  