﻿RELATION 
  OB^ 
  AQUATIC 
  PLANTS 
  TO 
  SUBSTRATUM. 
  493 
  

  

  Forel 
  (1902, 
  p. 
  183) 
  says: 
  "In 
  fact, 
  it 
  is 
  classical 
  in 
  botany 
  that 
  

   aquatic 
  plants 
  are 
  not 
  nourished 
  through 
  their 
  roots, 
  which 
  serve 
  only 
  

   as 
  organs 
  of 
  attachment; 
  they 
  have 
  no 
  need 
  of 
  humus. 
  Now, 
  however 
  

   unstable 
  the 
  sand 
  may 
  be, 
  it 
  seems 
  that 
  roots 
  sufficiently 
  deep 
  — 
  nearly 
  

   all 
  our 
  lacustrine 
  plants 
  have 
  roots 
  — 
  should 
  be 
  able 
  to 
  obtain 
  a 
  suffi- 
  

   cient 
  insertion 
  in 
  it. 
  This 
  fact, 
  added 
  to 
  the 
  well-known 
  case 
  of 
  Elodea 
  

   canadensis^ 
  which, 
  after 
  having 
  had 
  an 
  abundant 
  vegetation 
  during 
  

   the 
  first 
  period 
  of 
  its 
  invasion 
  of 
  a 
  new 
  territory, 
  becomes 
  reduced 
  to 
  

   relatively 
  modest 
  proportions 
  at 
  the 
  end 
  of 
  some 
  years 
  — 
  it 
  seems 
  that 
  

   it 
  has 
  exhausted 
  the 
  soil 
  — 
  ought 
  not 
  these 
  facts 
  to 
  engage 
  physiological 
  

   botanists 
  anew 
  in 
  a 
  study 
  of 
  the 
  dogma 
  that 
  the 
  roots 
  of 
  aquatic 
  plants 
  

   serve 
  only 
  as 
  organs 
  of 
  attachment? 
  It 
  may 
  be 
  possible, 
  however, 
  

   that 
  they 
  have 
  a 
  certain 
  nutritive 
  function 
  for 
  the 
  plant." 
  

  

  COMPARATIVE 
  STUDY 
  OF 
  GROWTH 
  UNDER 
  VARYING 
  CONDITIONS 
  

   OF 
  NUTRITION. 
  

  

  In 
  planning 
  the 
  experiments 
  for 
  this 
  part 
  of 
  the 
  work 
  it 
  was 
  

   assumed 
  that, 
  other 
  conditions 
  being 
  equal, 
  the 
  one 
  of 
  nutrition 
  deter- 
  

   mines 
  the 
  volume 
  of 
  vegetation 
  produced. 
  The 
  first 
  endeavor 
  was 
  to 
  

   determine 
  whether 
  the 
  soil 
  is 
  necessary 
  for 
  optimum 
  growth. 
  For 
  

   this 
  purpose 
  conditions 
  most 
  nearly 
  approaching 
  the 
  natural 
  ones 
  are 
  

   desirable, 
  and 
  these 
  are 
  easily 
  obtained 
  in 
  summer 
  by 
  means 
  of 
  float- 
  

   ing 
  aquaria, 
  which 
  are 
  described 
  in 
  detail 
  in 
  the 
  succeeding 
  pages. 
  

  

  If 
  the 
  soil 
  is 
  necessary 
  for 
  optimum 
  growth, 
  it 
  may 
  be 
  so 
  chiefly 
  for 
  

   two 
  reasons, 
  one 
  of 
  these 
  being 
  that 
  it 
  furnishes 
  nourishment, 
  the 
  

   other 
  that 
  it 
  serves 
  merely 
  as 
  a 
  substratum 
  in 
  which 
  plants 
  ma}^ 
  be 
  

   anchored. 
  In 
  the 
  former 
  case 
  the 
  roots 
  would 
  function 
  as 
  do 
  those 
  of 
  

   land 
  plants, 
  and 
  in 
  the 
  latter 
  merely 
  as 
  mechanical 
  holdfasts. 
  

  

  If 
  the 
  soil 
  serves 
  merely 
  as 
  a 
  substratum, 
  it 
  woukl 
  seem 
  that 
  clean 
  

   washed 
  sand 
  ought 
  to 
  do 
  equally 
  well. 
  -For 
  the 
  investigation 
  of 
  this 
  

   phase 
  of 
  the 
  problem 
  glass 
  aquaria 
  were 
  used, 
  and 
  in 
  these 
  the 
  efl'ects 
  

   of 
  sand 
  and 
  soil 
  substrata 
  on 
  growth 
  were 
  compared. 
  Further, 
  if 
  the 
  

   supernatant 
  water 
  tends 
  to 
  extract 
  nutritive 
  salts 
  from 
  the 
  soil, 
  the 
  

   water 
  above 
  humus 
  soil 
  ought 
  to 
  support 
  a 
  better 
  growth 
  of 
  plants 
  

   anchored 
  in 
  it 
  than 
  water 
  above 
  clean 
  washed 
  sand. 
  This 
  subject 
  has 
  

   also 
  received 
  attention, 
  and 
  the 
  methods 
  employed 
  will 
  be 
  described 
  

   later. 
  

  

  Again, 
  if 
  aquatics 
  do 
  absorb 
  salts 
  through 
  the 
  epidermis, 
  they 
  ought 
  

   to 
  make 
  an 
  optimum 
  growth 
  in 
  suitable 
  nutritive 
  solutions. 
  The 
  

   behavior 
  of 
  these 
  plants 
  in 
  culture 
  solutions 
  will 
  also 
  be 
  considered. 
  

  

  