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  REPOKT 
  OF 
  COMMISSIONER 
  OF 
  FISH 
  AND 
  FISHERIES. 
  

   RECAPITULATION 
  AND 
  THEORETICAL 
  DISCUSSION. 
  

  

  Seven 
  species 
  of 
  frequent 
  occurrence 
  in 
  our 
  aquatic 
  tiora 
  have 
  been 
  

   submitted 
  to 
  a 
  direct 
  test 
  to 
  determine 
  the 
  influence 
  of 
  a 
  soil 
  sub- 
  

   stratum 
  upon 
  their 
  growth. 
  In 
  live 
  of 
  these 
  cases 
  the 
  actual 
  growth 
  

   in 
  length 
  has 
  been 
  measured. 
  All 
  of 
  the 
  seven 
  species 
  grow 
  naturally 
  

   rooted 
  in 
  the 
  substratum. 
  Chara 
  has 
  only 
  rhizoids, 
  of 
  course, 
  but 
  

   the 
  others 
  have 
  roots, 
  and, 
  with 
  the 
  exception 
  of 
  Myriopliylluin, 
  root- 
  

   hairs 
  also. 
  Not 
  one 
  of 
  these 
  plants 
  can 
  make 
  an 
  optimum 
  growth 
  in 
  

   tap 
  water 
  if 
  the 
  roots 
  are 
  prevented 
  from 
  entering 
  the 
  substratum. 
  

   If 
  allowed 
  to 
  root 
  in 
  clean-washed 
  sand 
  a 
  better 
  growth 
  is 
  obtained, 
  

   but 
  not 
  nearly 
  so 
  good 
  as 
  when 
  the 
  roots 
  freely 
  penetrate 
  a 
  good 
  soil. 
  

   The 
  difference 
  in 
  amount 
  of 
  growth 
  between 
  plants 
  rooted 
  in 
  sand 
  

   and 
  those 
  in 
  soil, 
  in 
  terms 
  of 
  the 
  former, 
  was 
  for 
  Potamogeton 
  ^ 
  480.36 
  

   per 
  cent; 
  for 
  Elodea, 
  340.57 
  per 
  cent; 
  for 
  Banunculus^ 
  62.96 
  per 
  cent; 
  

   for 
  Myriophyllum^ 
  46.43 
  per 
  cent; 
  for 
  Chara^ 
  44.58. 
  No 
  reason 
  is 
  

   apparent 
  for 
  not 
  considering 
  these 
  figures 
  as 
  indicating 
  the 
  relative 
  

   dependence 
  of 
  the 
  different 
  species 
  upon 
  the 
  soil. 
  This 
  is, 
  however, 
  

   a 
  secondary 
  matter 
  as 
  compared 
  with 
  the 
  fact, 
  herein 
  demonstrated, 
  

   that 
  a 
  soil 
  substratum 
  is 
  requisite 
  for 
  normal 
  growth. 
  The 
  root- 
  

   development 
  of 
  the 
  anchored 
  plants 
  is 
  undoubtedly 
  retarded 
  by 
  

   exposure 
  to 
  light, 
  but, 
  as 
  is 
  shown 
  in 
  experiment 
  No. 
  17 
  (p. 
  515), 
  with 
  

   Ranimeidus^ 
  the 
  more 
  extensive 
  root-system 
  is 
  not 
  accompanied 
  by 
  a 
  

   correspondingly 
  greater 
  growth 
  in 
  stem 
  length. 
  Why 
  the 
  plants 
  

   rooted 
  in 
  sand 
  should 
  do 
  so 
  much 
  l)etter 
  than 
  those 
  anchored 
  above 
  

   sand 
  is 
  not 
  altogether 
  certain, 
  but 
  the 
  more 
  extensive 
  root-s3^stem 
  

   which 
  develops 
  in 
  sand 
  will 
  account 
  for 
  a 
  part 
  of 
  the 
  difference. 
  That 
  

   a 
  sand 
  substratum 
  10 
  or 
  15 
  cm. 
  deep 
  should 
  concentrate 
  the 
  salts 
  

   of 
  the 
  supernatant 
  water 
  to 
  a 
  degree 
  sufficient 
  to 
  influence 
  the 
  amount 
  

   of 
  growth 
  is 
  hardly 
  probable. 
  In 
  each 
  case 
  the 
  sand 
  was 
  thoroughly 
  

   clean 
  when 
  the 
  experiment 
  began, 
  but 
  some 
  undissolved 
  substance 
  

   ma}^ 
  have 
  ])ecome 
  embedded 
  in 
  it 
  during 
  the 
  experiment, 
  although 
  the 
  

   water 
  in 
  the 
  aquarium 
  was 
  frequently 
  stirred 
  and 
  siphoned 
  out. 
  

  

  In 
  experiment 
  No. 
  10 
  (p. 
  504) 
  sandy, 
  clayey, 
  and 
  loamy 
  soils 
  were 
  

   compared 
  with 
  respect 
  to 
  the 
  suitability 
  of 
  each, 
  and 
  it 
  appears 
  that 
  

   Vallisneria 
  and 
  Cham- 
  make 
  a 
  better 
  growth 
  on 
  a 
  good 
  loam 
  soil, 
  just 
  

   as 
  many 
  land 
  plants 
  do. 
  

  

  The 
  experiments 
  with 
  Sachs's 
  solution 
  show 
  that 
  the 
  plants 
  can 
  not 
  

   make 
  as 
  good 
  a 
  growth 
  in 
  it, 
  either 
  with 
  or 
  without 
  a 
  substratum, 
  as 
  

   in 
  soil 
  and 
  tap 
  water. 
  These 
  experiments 
  are 
  not 
  as 
  extensive 
  as 
  they 
  

   should 
  be 
  and 
  must 
  be 
  regarded 
  as 
  indicating 
  rather 
  than 
  establish- 
  

   ing 
  conclusions. 
  AVhat 
  is 
  the 
  most 
  suitable 
  solution 
  for 
  those 
  plants 
  

   and 
  whether 
  they 
  will 
  make 
  an 
  optimum 
  growth 
  in 
  any 
  solution 
  unless 
  

   rooted 
  in 
  a 
  substratum 
  must 
  be 
  left 
  as 
  open 
  questions. 
  The 
  suitability 
  

   of 
  Sachs's 
  solution 
  for 
  many 
  land 
  plants 
  is 
  well 
  known, 
  and 
  why 
  these 
  

   aquatics 
  should 
  be 
  unable 
  to 
  grow 
  in 
  it 
  can, 
  so 
  far 
  as 
  these 
  experi- 
  

  

  