﻿494 
  REPORT 
  OF 
  COMMISSIONER 
  OF 
  FISH 
  AND 
  FISHERIES. 
  

  

  INFLUENCE 
  OF 
  SUBSTRATUM. 
  

  

  VALIJSNEKIA 
  SPIRALIS. 
  

  

  This 
  plant 
  occurs 
  usually 
  in 
  water 
  from 
  15 
  cm. 
  to 
  3.5 
  m. 
  in 
  depth, 
  

   though 
  Evermann 
  (1902) 
  noted 
  it 
  growing 
  at 
  a 
  depth 
  of 
  22 
  feet. 
  It 
  

   thrives 
  also 
  in 
  shallow 
  running 
  water 
  where 
  a 
  soil 
  substratum 
  is 
  

   covered 
  by 
  a 
  shallow 
  stratum 
  of 
  gravel 
  and 
  the 
  water 
  remains 
  clear. 
  

   It 
  prefers 
  a 
  firm 
  soil 
  substratum 
  and 
  never 
  occurs 
  in 
  pure 
  gravel 
  or 
  

   sand, 
  but 
  its 
  roots 
  will 
  penetrate 
  a 
  thin 
  stratum 
  of 
  sand 
  or 
  gravel 
  to 
  

   soil 
  beneath, 
  and 
  it 
  may 
  be 
  found 
  rooted 
  in 
  the 
  soil 
  deposits 
  between 
  

   coarse 
  and 
  loosely 
  lying 
  stones. 
  The 
  roots 
  occur 
  as 
  tufts 
  at 
  the 
  nodes 
  

   of 
  the 
  creeping 
  rootstock, 
  are 
  fibrous, 
  unbranched, 
  and 
  clothed 
  with 
  

   root 
  hairs, 
  which 
  are 
  certainly 
  more 
  abundant 
  than 
  is 
  suggested 
  in 
  

   any 
  literature 
  that 
  has 
  come 
  to 
  my 
  notice. 
  Schwarz 
  (1881-1885) 
  states 
  

   that 
  one 
  may 
  examine 
  four 
  of 
  five 
  roots 
  of 
  Vallkneria 
  before 
  finding 
  

   rot)t 
  hairs. 
  My 
  observation 
  compels 
  me 
  to 
  differ 
  and 
  to 
  state 
  that 
  this 
  

   would 
  be 
  exceptional 
  if 
  the 
  plants 
  examined 
  were 
  carefully 
  removed 
  

   from 
  the 
  soil. 
  On 
  detached 
  and 
  floating 
  specimens 
  exposed 
  to 
  intense 
  

   light 
  the 
  root 
  hairs 
  soon 
  disappear 
  by 
  death 
  and 
  decay. 
  Schenck 
  

   (1886a) 
  states 
  that 
  Vallisnerla 
  and 
  Elodea 
  do 
  not 
  develop 
  root 
  hairs, 
  

   but 
  he 
  is 
  certainly 
  mistaken. 
  

  

  In 
  removing 
  specimens 
  from 
  the 
  soil 
  it 
  is 
  common 
  to 
  find 
  shells 
  

   pierced 
  by 
  the 
  roots 
  or 
  to 
  find 
  fragments 
  of 
  limestone 
  adhering 
  to 
  

   them, 
  so 
  it 
  is 
  quite 
  probable 
  that 
  the 
  roots 
  have 
  a 
  corrosive 
  effect 
  

   upon 
  these 
  insoluble 
  fragments 
  of 
  rock. 
  

  

  The 
  leaves 
  arise 
  from 
  the 
  creeping 
  rootstock, 
  and 
  the 
  older 
  ones 
  

   have 
  an 
  apical 
  opening 
  similar 
  to 
  that 
  described 
  by 
  Sauvageau 
  (1891) 
  

   for 
  some 
  other 
  aquatic 
  species. 
  The 
  opening 
  is 
  formed 
  by 
  disintegra- 
  

   tion 
  of 
  the 
  apical 
  tissue, 
  and 
  results 
  in 
  exposing 
  the 
  vascular 
  system 
  

   directl}^ 
  to 
  the 
  surrounding 
  medium. 
  In 
  ver}^ 
  young 
  leaves 
  this 
  open- 
  

   ing 
  could 
  not 
  be 
  found, 
  but 
  it 
  was 
  usually 
  present 
  in 
  leaves 
  25 
  cm. 
  or 
  

   more 
  in 
  length. 
  As 
  a 
  rule, 
  the 
  length 
  of 
  the 
  leaves 
  exceeds 
  the 
  depth 
  

   of 
  water 
  in 
  which 
  they 
  occur, 
  the 
  upper 
  portion 
  floating 
  horizontally 
  

   near 
  the 
  surface. 
  This 
  is 
  especially 
  true 
  when 
  the 
  plants 
  are 
  crowded 
  

   in 
  slowly 
  running 
  water. 
  In 
  the 
  latter 
  case 
  it 
  often 
  happens 
  that 
  the 
  

   leaves 
  exposed 
  to 
  the 
  intense 
  light 
  turn 
  brown 
  and 
  decay. 
  

  

  Experiment 
  No. 
  1. 
  — 
  This 
  experiment 
  was 
  conducted 
  at 
  the 
  laboratory 
  of 
  the 
  IT. 
  S. 
  

   Fish 
  Commission 
  at 
  Put-in 
  Bay, 
  Ohio, 
  during 
  the 
  period 
  of 
  four 
  weeks 
  from 
  July 
  

   18 
  to 
  August 
  18. 
  Floating 
  aquaria 
  were 
  constructed 
  as 
  follows: 
  Around 
  the 
  top 
  of 
  

   two 
  wooden 
  boxes 
  was 
  built 
  a 
  raft 
  large 
  enough 
  to 
  float 
  the 
  boxes, 
  the 
  latter 
  being 
  

   about 
  1 
  m. 
  wide, 
  1.5 
  m. 
  long, 
  and 
  75 
  cm. 
  deep. 
  In 
  one 
  box 
  was 
  placed 
  a 
  sub- 
  

   stratum 
  of 
  soil 
  selected 
  from 
  a 
  locality 
  in 
  which 
  VaUisnena 
  was 
  abundant. 
  The 
  

   aquaria 
  were 
  then 
  anchored 
  in 
  the 
  lake 
  and 
  weighted 
  so 
  that 
  they 
  floated, 
  submerged 
  

   a 
  few 
  centimeters 
  below 
  water 
  surface. 
  

  

  This 
  arrangement 
  furnished 
  the 
  closest 
  approximation 
  to 
  natural 
  conditions. 
  

   Wooden 
  bars 
  15 
  mm. 
  square 
  in 
  cross 
  section 
  and 
  a 
  little 
  less 
  than 
  1 
  m. 
  in 
  length 
  

  

  