﻿RELATION 
  OF 
  AQUATIC 
  PLANTS 
  TO 
  SUBSTRATUM. 
  499 
  

  

  growth 
  to 
  a 
  length 
  greatly 
  in 
  excess 
  of 
  the 
  former. 
  The 
  two 
  groups 
  

   of 
  anchored 
  plants 
  are 
  practically 
  equal 
  in 
  all 
  respects, 
  and 
  it 
  would 
  

   seem 
  that 
  the 
  water 
  over 
  sand 
  furnishes 
  as 
  much 
  nourishment 
  as 
  that 
  

   over 
  soil. 
  The 
  plants 
  rooted 
  in 
  sand 
  grew 
  better 
  than 
  those 
  anchored, 
  

   but 
  not 
  nearly 
  so 
  well 
  as 
  those 
  rooted 
  in 
  soil. 
  Lateral 
  roots 
  develop 
  

   abundantly 
  in 
  the 
  sand, 
  and 
  thus 
  those 
  plants, 
  had 
  a 
  much 
  more 
  exten- 
  

   sive 
  root 
  system. 
  

  

  The 
  following 
  percentages, 
  calculated 
  from 
  the 
  tables, 
  afford 
  a 
  con- 
  

   venient 
  summary 
  of 
  measurements 
  for 
  comparison. 
  An 
  allowance 
  of 
  

   10 
  per 
  cent 
  should 
  be 
  made 
  for 
  individual 
  variation 
  unaccounted 
  for. 
  

  

  Comparing 
  with 
  respect 
  to 
  total 
  length: 
  

  

  Plants 
  rooted 
  in 
  soil 
  exceed 
  plants 
  rooted 
  in 
  sand 
  62.96 
  per 
  cent 
  of 
  the 
  latter. 
  

  

  Plants 
  rooted 
  in 
  soil 
  exceed 
  plants 
  anchored 
  over 
  soil 
  195.20 
  per 
  cent 
  of 
  the 
  latter. 
  

  

  Plants 
  rooted 
  in 
  soil 
  exceed 
  plants 
  anchored 
  over 
  sand 
  174.18 
  per 
  cent 
  of 
  the 
  latter. 
  

  

  Plants 
  rooted 
  in 
  sand 
  exceed 
  plants 
  anchored 
  over 
  soil 
  81.15 
  per 
  cent 
  of 
  the 
  latter. 
  

  

  Plants 
  rooted 
  in 
  sand 
  exceed 
  plants 
  anchored 
  over 
  sand 
  68.25 
  per 
  cent 
  of 
  the 
  latter. 
  

  

  Plants 
  anchored 
  over 
  sand 
  exceed 
  plants 
  anchored 
  over 
  soil 
  7.66 
  per 
  cent 
  of 
  the 
  

   latter. 
  

  

  POTAMOGETON 
  PERFOLIATUS. 
  

  

  This 
  plant 
  grows 
  wholly 
  submerged 
  at 
  a 
  depth 
  varying 
  from 
  a 
  few 
  

   centimeters 
  to 
  a 
  meter. 
  It 
  is 
  most 
  abundant 
  in 
  protected 
  coves, 
  and 
  is 
  

   always 
  found 
  attached 
  to 
  a 
  substratum 
  containing 
  some 
  soil. 
  Loamy 
  

   soil 
  seems 
  to 
  be 
  its 
  first 
  choice, 
  but 
  a 
  fair 
  growth 
  is 
  often 
  attained 
  on 
  

   a 
  clayey 
  or 
  sandy 
  bottom. 
  The 
  plants 
  growing 
  in 
  very 
  shallow 
  

   water 
  seldom 
  fruit, 
  while 
  those 
  in 
  the 
  deeper 
  water 
  usually 
  do. 
  Vege- 
  

   tative 
  propagation 
  by 
  creeping 
  root-stocks 
  is 
  conspicuous. 
  The 
  leaves 
  

   are 
  thin, 
  broad, 
  with 
  clasping 
  base, 
  and 
  ribbed. 
  The 
  plants 
  appear 
  

   early 
  in 
  the 
  season 
  and 
  the 
  root-stocks 
  probably 
  remain 
  alive 
  through 
  

   the 
  winter. 
  The 
  growing 
  -root-stocks 
  will 
  turn 
  green 
  if 
  left 
  exposed 
  

   long 
  enough, 
  and 
  are 
  sensitive 
  to 
  either 
  light 
  or 
  gravitation 
  or 
  to 
  both. 
  

   If 
  a 
  cutting 
  of 
  the 
  erect 
  stem 
  be 
  suspended, 
  roots 
  do 
  not 
  arise 
  from 
  the 
  

   nodes 
  of 
  the 
  cutting, 
  but 
  instead 
  rhizomes 
  are 
  formed, 
  and 
  from 
  the 
  

   nodes 
  of 
  the 
  rhizomes 
  new 
  roots 
  arise. 
  The 
  roots 
  occur 
  as 
  fibrous 
  

   tufts 
  at 
  the 
  nodes 
  of 
  the 
  creeping 
  root-stock 
  and 
  are 
  unbranched. 
  

   Root 
  hairs 
  are 
  common, 
  but 
  not 
  so 
  abundant 
  as 
  in 
  Elodea 
  or 
  Ranunculus. 
  

  

  Experiment 
  No. 
  4- 
  — 
  The 
  location 
  and 
  conditions 
  remain 
  as 
  in 
  the 
  preceding 
  

   experiment, 
  the 
  duration 
  being 
  from 
  June 
  6 
  to 
  July 
  25. 
  In 
  this 
  case 
  the 
  aquaria 
  

   stood 
  outdoors 
  instead 
  of 
  in 
  the 
  greenhouse, 
  and 
  to 
  secure 
  a 
  cool 
  substratum 
  and 
  to 
  

   prevent 
  the 
  water 
  from 
  becoming 
  too 
  warm 
  they 
  Avere 
  sunk 
  10 
  cm. 
  into 
  the 
  earth. 
  

   It 
  was 
  also 
  found 
  necessary 
  to 
  protect 
  the 
  plants 
  from 
  intense 
  light, 
  and 
  this 
  was 
  

   done 
  by 
  shading 
  the 
  south 
  side 
  of 
  the 
  aquaria 
  with 
  felt 
  paper, 
  in 
  such 
  manner 
  that 
  

   the 
  plants 
  in 
  each 
  received 
  practically 
  the 
  same 
  amount 
  of 
  light. 
  Water 
  connec- 
  

   tions 
  were 
  made 
  with 
  a 
  hydrant, 
  so 
  that 
  fresh 
  water 
  could 
  be 
  supplied, 
  and 
  the 
  stale 
  

   water 
  was 
  siphoned 
  out 
  weekly. 
  

  

  Cuttings 
  of 
  terminal 
  portions 
  15 
  cm. 
  in 
  length 
  were 
  taken 
  from 
  young 
  and 
  fresh 
  

   river 
  plants, 
  and 
  10 
  were 
  placed 
  in 
  each 
  of 
  the 
  four 
  conditions 
  used 
  in 
  the 
  preceding 
  

   experiment. 
  These 
  cuttings 
  were 
  without 
  roots 
  or 
  rhizomes, 
  and, 
  in 
  distinction 
  from 
  

   the 
  new 
  growth 
  arising 
  from 
  them 
  during 
  the 
  experiment, 
  are 
  designated 
  "original 
  

   cuttings." 
  

  

  