﻿RELATION 
  OF 
  AQUATIC 
  PLANTS 
  TO 
  SUBSTRATUM. 
  497 
  

  

  The 
  roots 
  are 
  well 
  supplied 
  with 
  hairs; 
  those 
  arising 
  from 
  floating 
  

   fragments 
  are 
  often 
  almost 
  entirely 
  covered. 
  In 
  one 
  instance 
  a 
  root 
  

   was 
  found 
  to 
  be 
  clothed 
  with 
  hairs 
  for 
  a 
  distance 
  of 
  45 
  cm., 
  which 
  was 
  

   practically 
  its 
  whole 
  length. 
  The 
  roots 
  are 
  strongly 
  geotropic, 
  and 
  

   always 
  regain 
  the 
  vertical 
  position 
  if 
  displaced 
  from 
  it. 
  

   - 
  In 
  each 
  of 
  the 
  following 
  experiments 
  two 
  rectangular 
  glass 
  aquaria 
  

   of 
  about 
  50 
  liters 
  capacity 
  were 
  used. 
  One 
  of 
  these 
  contained 
  a 
  sub- 
  

   stratum 
  of 
  suitable 
  soil 
  from 
  the 
  bed 
  of 
  a 
  stream 
  and 
  the 
  other 
  con- 
  

   tained 
  thoroughly 
  cleaned 
  sand. 
  Considerable 
  pains 
  were 
  taken 
  to 
  

   remove 
  all 
  the 
  soil 
  particles 
  from 
  the 
  sand, 
  which 
  was 
  accomplished 
  

   b3r 
  first 
  washing 
  it 
  as 
  clean 
  as 
  possible, 
  then 
  allowing 
  it 
  to 
  soak 
  for 
  

   several 
  hours 
  and 
  again 
  washing 
  it, 
  this 
  process 
  being 
  continued 
  until 
  

   the 
  sand 
  was 
  entirely 
  clean. 
  

  

  A 
  certain 
  number 
  of 
  cuttings 
  from 
  the 
  stock 
  aquaria 
  were 
  planted 
  

   in 
  the 
  substratum 
  in 
  one 
  end 
  of 
  each 
  aquarium, 
  and 
  in 
  the 
  other 
  end 
  

   a 
  like 
  number 
  of 
  cuttings 
  were 
  anchored 
  in 
  the 
  supernatant 
  water. 
  

   To 
  keep 
  these 
  suspended 
  cuttings 
  wholl}- 
  submerged 
  and 
  in 
  vertical 
  

   position 
  a 
  small 
  piece 
  of 
  glass 
  tubing 
  was 
  attached 
  by 
  a 
  short 
  cord 
  to 
  

   the 
  basal 
  node 
  of 
  the 
  cutting. 
  Cr3^stallizing 
  dishes 
  received 
  the 
  roots 
  

   that 
  developed 
  from 
  the 
  suspended 
  cuttings 
  and 
  prevented 
  their 
  con- 
  

   tact 
  with 
  the 
  substratum. 
  By 
  means 
  of 
  a 
  siphon 
  the 
  water 
  in 
  each 
  

   aquarium 
  was 
  removed 
  on 
  an 
  average 
  of 
  about 
  once 
  a 
  week, 
  fresh 
  

   water 
  being 
  allowed 
  to 
  enter 
  from 
  the 
  tap 
  above 
  the 
  aquarium 
  as 
  the 
  

   stale 
  water 
  siphoned 
  out. 
  In 
  this 
  way 
  a 
  complete 
  renewal 
  of 
  water 
  

   was 
  effected 
  without 
  injury 
  or 
  disturbance 
  to 
  the 
  plants. 
  

  

  Experiment 
  No. 
  3.— 
  In 
  this 
  instance 
  the 
  aquaria 
  were 
  located 
  in 
  the 
  greenhouse 
  at 
  

   Ann 
  Arbor. 
  The 
  temperature 
  varied 
  from 
  16° 
  to 
  22° 
  C, 
  and 
  many 
  of 
  the 
  days 
  were 
  

   cloudy. 
  The 
  duration 
  of 
  the 
  test 
  was 
  from 
  January 
  2 
  to 
  March 
  5, 
  a 
  period 
  of 
  about 
  

   sixty 
  days. 
  Terminal 
  portions 
  of 
  plants 
  from 
  the 
  stock 
  aquarium 
  were 
  selected, 
  and 
  

   10 
  such 
  cuttings 
  of 
  uniform 
  length 
  and 
  quality, 
  having 
  neither 
  branches 
  nor 
  roots, 
  

   were 
  placed 
  in 
  each 
  of 
  the 
  four 
  conditions 
  previously 
  mentioned. 
  After 
  a 
  period 
  

   of 
  sixty-one 
  days 
  positive 
  differences 
  in 
  the 
  growth 
  of 
  the 
  four 
  groups 
  could 
  be 
  

   observed. 
  

  

  F. 
  C. 
  1903—32 
  

  

  