﻿RELATION 
  OF 
  AQUATIC 
  PLANTS 
  TO 
  SUBSTRATUM. 
  

  

  515 
  

  

  LIGHT 
  AND 
  MECHANICAL 
  CONTACT 
  AS 
  FACTORS 
  IN 
  THE 
  

   DEVELOPMENT 
  OF 
  LATERAL 
  ROOTS. 
  

  

  EANUNCrLUS 
  AQUATILIS 
  TRICHOPHYLLUS. 
  

  

  It 
  has 
  been 
  noted 
  that 
  when 
  fragments 
  of 
  this 
  plant 
  are 
  left 
  floating-, 
  

   the 
  new 
  roots 
  arising 
  at 
  the 
  nodes 
  grow 
  directly 
  downward 
  and 
  do 
  not 
  

   branch 
  until 
  entering 
  a 
  substratum. 
  

  

  Three 
  conditions 
  suggest 
  themselves 
  as 
  possible 
  factors 
  in 
  determin- 
  

   ing 
  the 
  development 
  of 
  these 
  lateral 
  roots. 
  The 
  first 
  is 
  light; 
  the 
  

   second, 
  mechanical 
  contact 
  as 
  a 
  stimulus; 
  the 
  third, 
  a 
  difference 
  of 
  

   osmotic 
  strength 
  between 
  the 
  solution 
  in 
  the 
  soil 
  and 
  that 
  above 
  it. 
  

   The 
  last 
  supposition 
  is 
  very 
  improbable, 
  as 
  lateral 
  roots 
  develop 
  

   abundantly 
  in 
  clean 
  washed 
  sand, 
  and 
  in 
  this 
  case 
  the 
  roots 
  are 
  proba- 
  

   bl}' 
  exposed 
  to 
  a 
  solution 
  whose 
  osmotic 
  strength 
  is 
  the 
  same 
  as 
  that 
  of 
  

   the 
  solution 
  above 
  the 
  sand. 
  The 
  following 
  test 
  was 
  made 
  with 
  a 
  view 
  

   of 
  ascertaining 
  the 
  determining 
  factor: 
  

  

  Experiment 
  Xo. 
  17. 
  — 
  This 
  experiment 
  was 
  conducted 
  in 
  the 
  greenhouse 
  from 
  April 
  

   10 
  to 
  May 
  18. 
  Fresh 
  cuttings, 
  25 
  cm. 
  in 
  length, 
  were 
  mounted 
  in 
  10-ounce 
  bottles, 
  

   submerged 
  in 
  tap 
  water 
  contained 
  in 
  cylindrical 
  battery 
  jars. 
  A 
  loose 
  cotton 
  stopper 
  

   wrapped 
  about 
  the 
  cutting 
  kept 
  it 
  in 
  proper 
  position, 
  and 
  did 
  not 
  prevent 
  the 
  diffu- 
  

   sion 
  of 
  water 
  inside 
  the 
  bottle 
  with 
  that 
  outside. 
  Four 
  conditions 
  entered 
  into 
  the 
  

   test: 
  Bottles 
  wrapped 
  in 
  black 
  cloth 
  to 
  exclude 
  hght; 
  bottles 
  not 
  covered, 
  roots 
  being 
  

   exposed 
  to 
  light; 
  bottles 
  not 
  covered, 
  but 
  containing 
  sand, 
  and 
  bottles 
  not 
  covered, 
  

   but 
  containing 
  granulated 
  glass. 
  

  

  About 
  three 
  nodes 
  of 
  the 
  cutting 
  were 
  inside 
  the 
  bottle 
  in 
  each 
  case, 
  and 
  when 
  

   first 
  mounted 
  the 
  cuttings 
  were 
  without 
  roots. 
  Five 
  cuttings 
  were 
  in 
  conditions 
  

   1 
  and 
  2, 
  and 
  3 
  cuttings 
  in 
  conditions 
  4 
  and 
  5. 
  In 
  No. 
  4 
  the 
  intention 
  was 
  to 
  have 
  

   mechanical 
  contact 
  with 
  a 
  transparent 
  substratum, 
  ])ut 
  a 
  layer 
  of 
  glass 
  deep 
  enough 
  

   for 
  a 
  substratum 
  greatly 
  reduces 
  the 
  light. 
  In 
  no 
  case 
  did 
  roots 
  from 
  nodes 
  above 
  

   the 
  stopper 
  have 
  lateral 
  branches, 
  and, 
  as 
  the 
  number 
  of 
  these 
  roots 
  was 
  practically 
  

   equal 
  to 
  the 
  number 
  arising 
  from 
  nodes 
  below 
  the 
  stopper, 
  only 
  the 
  latter 
  are 
  given 
  

   in 
  the 
  table. 
  

  

  Influence 
  of 
  light 
  on 
  the 
  development 
  of 
  root 
  system 
  of 
  Ranunculus 
  agualUls 
  trichopliyllus. 
  

  

  These 
  figures 
  show 
  (1) 
  that, 
  other 
  conditions 
  being 
  ccj[ual, 
  light 
  

   inhibits 
  the 
  formation 
  of 
  lateral 
  roots 
  and 
  retards 
  the 
  growth 
  of 
  main 
  

   roots; 
  (2) 
  that 
  plants 
  with 
  roots 
  in 
  wrapped 
  bottles 
  and 
  consequently 
  

   a 
  more 
  extensive 
  root 
  system 
  do 
  not 
  make 
  a 
  proportionateh^ 
  greater 
  

   growth 
  in 
  steiu 
  length. 
  The 
  remaining 
  figures 
  are 
  of 
  little 
  value 
  as 
  

   they 
  stand. 
  

  

  