﻿RELATION 
  OF 
  AQUATIC 
  PLANTS 
  TO 
  SUBSTRATUM. 
  5l7 
  

  

  ments 
  have 
  gone, 
  be 
  only 
  surmised. 
  It 
  is 
  noteworth}^ 
  that 
  in 
  the 
  

   absence 
  of 
  a 
  substratum 
  Sachs's 
  solution 
  totally 
  inhibits 
  root 
  forma- 
  

   tion 
  in 
  the 
  case 
  of 
  Elodea; 
  with 
  Potamogeton 
  a 
  very 
  few 
  roots 
  appear, 
  

   but 
  shortl.y 
  die; 
  with 
  Ranunculus 
  more 
  roots 
  appear, 
  but 
  they 
  reach 
  

   a 
  length 
  of 
  only 
  a 
  few 
  centimeters. 
  All 
  of 
  these 
  plants 
  will 
  develop 
  

   roots 
  better 
  in 
  Sachs's 
  solution 
  if 
  allowed 
  to 
  send 
  them 
  into 
  a 
  sand 
  sub- 
  

   stratum, 
  but 
  even 
  here 
  the 
  development 
  is 
  much 
  less 
  than 
  with 
  plants 
  

   anchored 
  in 
  tap 
  water 
  without 
  a 
  substratum. 
  It 
  is 
  evident 
  that 
  the 
  

   sand 
  substratum, 
  as 
  well 
  as 
  the 
  solution 
  and 
  light, 
  is 
  a 
  factor 
  influen- 
  

   cing- 
  root 
  development, 
  unless 
  we 
  assume 
  that 
  the 
  sand 
  changes 
  the 
  

   strength 
  or 
  quality 
  of 
  that 
  part 
  of 
  the 
  solution 
  which 
  saturates 
  it. 
  

   True 
  and 
  Oglevee 
  (1904) 
  found 
  that 
  the 
  presence 
  of 
  insoluble 
  sub- 
  

   stances, 
  such 
  as 
  sand, 
  paraffin, 
  and 
  filter 
  paper, 
  in 
  solutions 
  "exerts 
  

   an 
  effect 
  closely 
  paralleling 
  that 
  of 
  simple 
  dilution.'' 
  As 
  the 
  Sachs's 
  

   solution 
  was 
  frequently 
  renewed 
  we 
  can 
  not 
  suppose 
  that 
  the 
  quality 
  

   of 
  the 
  solution 
  gradually 
  became 
  unfavorable 
  during 
  the 
  experiment. 
  

   In 
  experiment 
  No. 
  13 
  (p. 
  508), 
  where 
  Ranimcuhis 
  is 
  grown 
  in 
  Sachs's 
  

   solution 
  without 
  a 
  substratum, 
  with 
  a 
  sand 
  substratum, 
  and 
  with 
  a 
  

   soil 
  substratum, 
  we 
  see 
  that 
  the 
  soil 
  here 
  is 
  a 
  very 
  important 
  factor. 
  

   The 
  average 
  length 
  in 
  the 
  three 
  groups 
  was 
  19.16 
  cm., 
  18.8 
  cm., 
  and 
  26 
  

   cm., 
  respectively. 
  This 
  brings 
  out 
  the 
  interesting 
  fact 
  that 
  the 
  soil 
  

   in 
  some 
  way 
  helps 
  the 
  plant 
  under 
  otherwise 
  unfavorable 
  conditions. 
  

  

  That 
  the 
  roots 
  of 
  most 
  of 
  our 
  common 
  aquatics 
  are 
  provided 
  w^ith 
  

   root 
  hairs 
  is 
  significant, 
  and 
  certainly 
  indicates 
  that 
  absorption 
  is 
  an 
  

   important 
  function 
  of 
  the 
  roots. 
  It 
  is 
  interesting 
  to 
  note 
  in 
  this 
  con- 
  

   nection 
  that 
  of 
  the 
  two 
  species 
  found 
  to 
  be 
  least 
  dependent 
  upon 
  the 
  

   soil, 
  one 
  is 
  Chara^ 
  an 
  alga 
  with 
  only 
  rhizoids 
  instead 
  of 
  roots, 
  and 
  the 
  

   other 
  Myp'iopliylhim^ 
  which 
  has 
  roots, 
  but 
  not 
  root 
  hairs. 
  

  

  Experiments 
  11 
  and 
  15 
  (pp, 
  510 
  and 
  511) 
  demonstrate 
  that 
  the 
  roots 
  

   will 
  absorb 
  lithium 
  nitrate 
  and 
  that 
  the 
  salt 
  is 
  carried 
  upward 
  into 
  the 
  

   stem 
  and 
  leaves. 
  Reference 
  to 
  the 
  experiment 
  will 
  show 
  that 
  diffusion 
  

   will 
  not 
  account 
  for 
  this 
  result 
  and 
  there 
  is 
  no 
  escape 
  from 
  the 
  conclu- 
  

   sion 
  that 
  an 
  upward 
  current 
  carries 
  the 
  salt 
  to 
  the 
  leaves. 
  

  

  Experiment 
  16 
  (p. 
  511) 
  demonstrates 
  the 
  absorption 
  of 
  a 
  given 
  amount 
  

   of 
  tap 
  water 
  in 
  a 
  given 
  time 
  by 
  the 
  roots 
  developed 
  from 
  cuttings 
  sus- 
  

   pended 
  in 
  tap 
  water. 
  It 
  was 
  not 
  intended 
  here 
  to 
  determine 
  the 
  rate 
  

   of 
  absorption, 
  but 
  only 
  to 
  demonstrate 
  the 
  fact. 
  It 
  is 
  to 
  be 
  regretted 
  

   that 
  the 
  several 
  attempts 
  made 
  to 
  measure 
  the 
  exudation 
  from 
  the 
  stem 
  

   and 
  leaves 
  were 
  unsuccessful. 
  Hochreutiner's 
  efforts 
  to 
  do 
  the 
  same 
  

   thing 
  were 
  not 
  rewarded 
  by 
  results 
  because 
  of 
  the 
  difficulties 
  encoun- 
  

   tered 
  in 
  the 
  technique. 
  If, 
  however, 
  a 
  large 
  absorption 
  is 
  a 
  fact, 
  the 
  

   exudation 
  is 
  a 
  necessar}^ 
  consequence. 
  Whether 
  this 
  exudation 
  is 
  in 
  

   any 
  way 
  comparable 
  to 
  the 
  transpiration 
  of 
  terrestrial 
  plants 
  is 
  an 
  inter- 
  

   esting 
  and 
  relevant 
  question, 
  but 
  the 
  answer 
  to 
  such 
  an 
  inquiry 
  is 
  not 
  

   considered 
  possible 
  on 
  the 
  basis 
  of 
  these 
  experiments. 
  

  

  