﻿488 
  REPORT 
  OF 
  COMMISSIONER 
  OF 
  FISH 
  AND 
  FISHERIES. 
  

  

  the 
  chain 
  of 
  nutritive 
  relations 
  leads 
  us 
  throug-h 
  the 
  smaller 
  animals 
  

   chiefly 
  to 
  the 
  microscopic 
  plants, 
  which 
  depend 
  for 
  their 
  food 
  supply 
  

   upon 
  the 
  carbon 
  dioxid 
  and 
  various 
  other 
  substances 
  in 
  solution 
  in 
  the 
  

   water. 
  The 
  presence 
  of 
  the 
  other 
  substances 
  is 
  due 
  to 
  various 
  causes; 
  

   they 
  are 
  brought 
  by 
  tributary 
  streams 
  and 
  by 
  the 
  erosion 
  of 
  the 
  

   shores; 
  they 
  are 
  washed 
  in 
  from 
  the 
  air 
  by 
  rains, 
  and 
  they 
  come 
  from 
  

   numerous 
  accidental 
  sources. 
  In 
  solution 
  in 
  the 
  water 
  they 
  are 
  the 
  

   ultimate 
  sources 
  of 
  food 
  for 
  fish; 
  yet 
  neither 
  fish 
  nor 
  the 
  animals 
  upon 
  

   which 
  fish 
  feed 
  can 
  secure 
  nourishment 
  from 
  these 
  sources 
  directly. 
  

   Plants 
  must 
  intervene 
  to 
  organize 
  the 
  mineral 
  salts 
  and 
  carbon 
  dioxid 
  

   of 
  the 
  water 
  into 
  food. 
  

  

  The 
  aquatic 
  plants 
  may 
  be 
  considered 
  in 
  two 
  g-roups, 
  one 
  including 
  

   those 
  which 
  are 
  attached 
  to 
  the 
  soil 
  by 
  roots 
  and 
  the 
  other 
  comprising 
  

   those 
  which 
  float 
  free 
  or 
  are 
  without 
  organs 
  of 
  attachment. 
  The 
  latter 
  

   are 
  mostly 
  microscopic, 
  and 
  taken 
  together 
  are 
  designated 
  as 
  the 
  vege- 
  

   table 
  plankton 
  or 
  phyto-plankton 
  in 
  distinction 
  from 
  the 
  minute 
  free- 
  

   swimming 
  animals, 
  which 
  as 
  a 
  whole 
  are 
  spoken 
  of 
  as 
  animal 
  plankton 
  

   or 
  zoo-plankton. 
  In 
  the 
  case 
  of 
  the 
  free 
  plants, 
  food 
  must 
  be 
  obtained 
  

   from 
  the 
  water 
  which 
  surrounds 
  them, 
  and 
  a 
  deficiency 
  of 
  any 
  one 
  of 
  

   the 
  substances 
  now 
  known 
  to 
  be 
  essential 
  for 
  plant 
  growth 
  means 
  a 
  

   reduced 
  quantity 
  of 
  vegetable 
  plankton, 
  and 
  consequently 
  a 
  limited 
  

   food 
  supply 
  for 
  the 
  fish. 
  The 
  forms 
  of 
  the 
  phyto-plankton 
  require 
  

   nitrogen, 
  potash, 
  and 
  phosphoric 
  acid 
  just 
  as 
  other 
  plants 
  do, 
  and 
  

   Brandt 
  (1899) 
  has 
  based 
  upon 
  the 
  work 
  of 
  Apstein 
  the 
  statement 
  that 
  

   the 
  amount 
  of 
  plankton 
  varies 
  directly 
  with 
  the 
  proportion 
  of 
  nitrates 
  

   dissolved 
  in 
  the 
  water. 
  The 
  view 
  hitherto 
  usually 
  held 
  has 
  been 
  that 
  

   the 
  rooted 
  aquatic 
  plants 
  also 
  take 
  their 
  nourishment 
  directly 
  from 
  the 
  

   water 
  and 
  not 
  at 
  all 
  from 
  the 
  soil; 
  that 
  their 
  roots 
  consequently 
  are 
  

   organs 
  of 
  attachment 
  only, 
  not 
  organs 
  for 
  drawing 
  nutrition 
  from 
  the 
  

   soil. 
  If 
  this 
  be 
  true 
  the 
  larger 
  aquatics 
  must, 
  during 
  the 
  growing 
  

   season, 
  withdraw 
  from 
  the 
  water 
  large 
  quantities 
  of 
  nutritive 
  sub- 
  

   stances 
  which 
  would 
  otherwise 
  be 
  available 
  for 
  the 
  phyto-plankton, 
  

   thus 
  lessening 
  the 
  amount 
  of 
  phyto-plankton 
  tiiat 
  the 
  water 
  is 
  capable 
  

   of 
  producing 
  during 
  this 
  period, 
  and 
  consequent!}' 
  lessening 
  the 
  supply 
  

   of 
  fish-food 
  dependent 
  on 
  this 
  phyto-plankton. 
  By 
  the 
  subsequent 
  

   decay 
  of 
  these 
  larger 
  aquatics 
  the 
  food 
  materials 
  withdrawn 
  by 
  them 
  

   from 
  the 
  water 
  would 
  be 
  returned 
  to 
  it 
  and 
  made 
  available 
  for 
  the 
  

   phyto-plankton; 
  but 
  while 
  they 
  would 
  thus 
  on 
  the 
  average 
  not 
  lessen, 
  

   they 
  would, 
  on 
  the 
  other 
  hand, 
  not 
  increase 
  the 
  supply 
  of 
  food 
  for 
  the 
  

   phyto-plankton. 
  

  

  if, 
  however, 
  the 
  view 
  just 
  expressed 
  be 
  incorrect, 
  and 
  if 
  the 
  larger 
  

   aquatics 
  draw 
  their 
  supply 
  of 
  mineral 
  food 
  not 
  from 
  the 
  water 
  but 
  

   from 
  the 
  soil, 
  they 
  draw 
  upon 
  a 
  source 
  which 
  is 
  not 
  available 
  for 
  the 
  

   phyto-plankton. 
  Their 
  growth, 
  then, 
  does 
  not 
  at 
  any 
  time 
  lessen 
  the 
  

   supply 
  of 
  phyto-plankton; 
  on 
  the 
  contrary 
  when 
  the 
  larger 
  aquatics 
  

  

  