﻿RELATION 
  OF 
  AQUATIC 
  PLANTS 
  TO 
  SUBSTRATUM. 
  

  

  509 
  

  

  substratum 
  being 
  suspended 
  and 
  anchored 
  with 
  bits 
  of 
  glass 
  tubing 
  attached. 
  The 
  

   accompanying 
  table 
  shows 
  the 
  increase 
  in 
  length 
  of 
  the 
  plants 
  after 
  a 
  period 
  of 
  

   34 
  days: 
  

  

  Grouih 
  measureinent 
  of 
  Ranunculus 
  aquatilis 
  trichophyllus 
  at 
  the 
  end 
  of 
  34 
  days. 
  

   Original 
  length 
  of 
  each 
  cutting, 
  10 
  cm. 
  

  

  These 
  figures 
  show 
  that 
  a 
  soil 
  substratum 
  favors 
  the 
  growth 
  even 
  in 
  

   a 
  nutrient 
  medium 
  which 
  contains 
  all 
  the 
  necessarv 
  nourishment. 
  

  

  Sachs's 
  solution 
  inhibits 
  the 
  root 
  development 
  here 
  also, 
  but 
  not 
  

   nearly 
  so 
  much 
  as 
  with 
  Elodea 
  and 
  Potaiiiogeton. 
  As 
  all 
  three 
  of 
  these 
  

   plants 
  develop 
  roots 
  abundantly 
  in 
  tap 
  water 
  without 
  a 
  substratum, 
  we 
  

   may 
  suppose 
  that 
  Sachs's 
  solution 
  contains 
  ingredients 
  which 
  are 
  

   unsuitable, 
  at 
  least 
  in 
  the 
  given 
  proportion. 
  While 
  it 
  is 
  true 
  that 
  in 
  

   all 
  my 
  experiments 
  a 
  good 
  plant 
  growth 
  is 
  accompanied 
  by 
  a 
  well- 
  

   developed 
  root 
  system, 
  it 
  will 
  lie 
  remembered 
  that 
  in 
  the 
  aquarium 
  

   experiments 
  with 
  Ham/ncub/.s 
  the 
  plants 
  rooted 
  in 
  sand 
  had 
  a 
  good 
  root 
  

   S3"stem, 
  but 
  not 
  a 
  corresponding 
  growth 
  of 
  stem. 
  Although 
  Sachs's 
  

   solution 
  may 
  be 
  regarded 
  as 
  unfavorable 
  for 
  root 
  development, 
  we 
  can 
  

   not 
  attribute 
  the 
  retarded 
  growth 
  of 
  the 
  plant 
  to 
  an 
  injurious 
  effect 
  

   from 
  it 
  unless 
  we 
  assume 
  that 
  the 
  injury 
  is 
  neutralized 
  by 
  the 
  soil, 
  for 
  

   we 
  get 
  a 
  much 
  better 
  growth 
  in 
  Sachs's 
  solution 
  over 
  a 
  soil 
  substratum. 
  

  

  SIGNIFICANCE 
  AND 
  DISTRIBUTION 
  OF 
  ROOT 
  HAIRS. 
  

  

  Since 
  a 
  root 
  hair 
  is 
  merely 
  a 
  peripheral 
  root 
  cell 
  protruded, 
  the 
  

   interpretation 
  generally 
  accepted 
  for 
  this 
  structure 
  is 
  that 
  it 
  serves 
  to 
  

   increase 
  the 
  absorbing 
  surface 
  of 
  the 
  root. 
  If 
  this 
  is 
  correct, 
  and 
  the 
  

   roots 
  of 
  aquatic 
  plants 
  are 
  only 
  for 
  mechanical 
  attachment, 
  a 
  root 
  hair 
  

   would 
  seem 
  to 
  be 
  an 
  unnecessary 
  structure 
  in 
  such 
  .species. 
  

  

  Many 
  authors 
  have 
  made 
  much 
  of 
  the 
  fact 
  that 
  submerged 
  aquatics 
  

   show 
  a 
  very 
  rudimentary 
  vascular 
  system 
  and 
  that 
  their 
  anatomy 
  indi- 
  

   cates 
  that 
  absorption 
  is 
  not 
  a 
  specialized 
  function 
  of 
  the 
  plant. 
  Per- 
  

   haps 
  this 
  is 
  somewhat 
  justifiable, 
  but 
  have 
  we 
  not 
  in 
  the 
  presence 
  of 
  

   root 
  hairs 
  reason 
  for 
  a 
  different 
  opinion? 
  These 
  are 
  such 
  simple 
  

   structures 
  that 
  they 
  would 
  not 
  be 
  likely 
  to 
  be 
  developed 
  very 
  long 
  

   after 
  becoming 
  unnecessary; 
  i. 
  e., 
  after 
  the 
  plants 
  bearing 
  them 
  had 
  

   passed 
  from 
  terrestial 
  to 
  aquatic 
  habits. 
  

  

  