﻿RELATION 
  OF 
  AQUATIC 
  PLANTS 
  TO 
  SUBSTRATUM. 
  519 
  

  

  processes, 
  in 
  which 
  the 
  soil 
  tends 
  to 
  withdraw 
  salts 
  from 
  solution, 
  and 
  

   the 
  water 
  tends 
  to 
  bring 
  salts 
  of 
  the 
  soil 
  into 
  solution. 
  Excluding 
  

   other 
  factors, 
  these 
  two 
  processes 
  would 
  probably 
  establish 
  an 
  equi- 
  

   librium 
  resulting 
  in 
  a 
  constant 
  concentration. 
  But 
  plants, 
  and 
  espe- 
  

   cially 
  those 
  attached 
  to 
  the 
  soil, 
  are 
  important 
  factors 
  in 
  the 
  redistri- 
  

   bution 
  of 
  matter, 
  which 
  is 
  constantl}" 
  going 
  on. 
  The 
  roots 
  in 
  respi- 
  

   ration 
  excrete 
  carbon 
  dioxide, 
  which 
  helps 
  to 
  bring 
  otherwise 
  insoluble 
  

   salts 
  into 
  solution. 
  

  

  Apparently 
  the 
  substances 
  needed 
  by 
  the 
  plants 
  are 
  the 
  ones 
  most 
  

   firmly 
  retained 
  by 
  the 
  soil, 
  and 
  yet 
  it 
  can 
  not 
  be 
  said 
  that 
  the 
  water 
  

   does 
  not 
  contain 
  enough 
  of 
  these 
  salts 
  for 
  the 
  larger 
  plants. 
  That 
  

   plants 
  have 
  a 
  quantitative 
  selective 
  power 
  is 
  certain, 
  and 
  their 
  capacity 
  

   for 
  concentrating 
  salts 
  from 
  very 
  dilute 
  solutions 
  is 
  well 
  established, 
  

   especiall}' 
  in 
  the 
  case 
  of 
  potassium 
  in 
  land 
  plants 
  and 
  of 
  iodine 
  in 
  

   some 
  marine 
  forms. 
  Liebig 
  (1858, 
  p. 
  110) 
  found 
  that 
  the 
  ash 
  of 
  

   Lemna 
  contained 
  of 
  potassium 
  13.16 
  per 
  cent 
  and 
  of 
  phosphoric 
  acid 
  

   8.73 
  per 
  cent, 
  while 
  the 
  inorganic 
  residue 
  from 
  the 
  water 
  in 
  which 
  the 
  

   Lemna 
  was 
  growing 
  contained 
  these 
  substances 
  in 
  the 
  respective 
  pro- 
  

   portions 
  of 
  3.97 
  per 
  cent 
  and 
  2.619 
  per 
  cent. 
  As 
  Lemna 
  and 
  Cera- 
  

   tojyhyllum 
  must 
  derive 
  their 
  mineral 
  nourishment 
  exclusively 
  from 
  the 
  

   water, 
  it 
  is 
  evident 
  that 
  the 
  necessary 
  salts 
  are 
  present, 
  and 
  in 
  suffi- 
  

   cient 
  quantity 
  for 
  some 
  plants. 
  

  

  Granted, 
  then, 
  that 
  the 
  necessary 
  salts 
  are 
  present, 
  though 
  in 
  very 
  

   small 
  quantity 
  in 
  some 
  cases, 
  it 
  may 
  next 
  be 
  asked: 
  Are 
  the 
  salts 
  present 
  

   in 
  suitable 
  proportion? 
  The 
  evidence 
  at 
  hand 
  hardly 
  furnishes 
  satis- 
  

   factory 
  reply. 
  Chemical 
  analysis 
  of 
  ValUsneria 
  indicates 
  that 
  they 
  

   are 
  not. 
  The 
  marked 
  excess 
  of 
  calcium 
  and 
  magnesium 
  in 
  the 
  anchored 
  

   plants 
  is 
  a 
  noteworthj^ 
  fact. 
  According 
  to 
  Loew's 
  (1901, 
  p. 
  16) 
  hypothe- 
  

   sis, 
  calcium 
  is 
  especially 
  required 
  for 
  the 
  formation 
  of 
  nucleoproteids 
  

   and 
  magnesium 
  for 
  facilitating 
  the 
  assimilation 
  of 
  phosphoric 
  acid. 
  

   Should 
  the 
  excess 
  of 
  lime 
  be 
  too 
  great, 
  the 
  magnesium 
  is 
  displaced 
  and 
  

   the 
  phosphoric 
  acid, 
  combining 
  with 
  the 
  lime, 
  becomes 
  insoluble. 
  The 
  

   result 
  (Loew, 
  1901) 
  is 
  the 
  same 
  as 
  if 
  the 
  supply 
  of 
  phosphoric 
  acid 
  were 
  

   too 
  limited, 
  and 
  the 
  plant 
  succumbs 
  to 
  starvation. 
  Loew's 
  hypothesis 
  

   is 
  hardl}^ 
  applicable 
  to 
  my 
  results, 
  however, 
  as 
  the 
  ratio 
  of 
  magnesium 
  

   to 
  calcium 
  in 
  plants 
  rooted 
  in 
  soil 
  is 
  about 
  the 
  same 
  as 
  that 
  in 
  the 
  

   anchored 
  plants. 
  

  

  The 
  accumulation 
  of 
  starch 
  in 
  the 
  anchored 
  plants 
  is 
  the 
  most 
  posi- 
  

   tive 
  evidence 
  of 
  abnormal 
  metabolism 
  revealed 
  by 
  the 
  chemical 
  analy- 
  

   sis, 
  and 
  this, 
  in 
  connection 
  with 
  the 
  retarded 
  growth, 
  furnishes 
  a 
  basis 
  

   for 
  further 
  investigation. 
  Is 
  the 
  growth 
  retarded 
  because 
  the 
  starch 
  

   is 
  formed 
  too 
  rapidl}^, 
  or 
  does 
  the 
  starch 
  accumulate 
  because 
  growth 
  

   is 
  retarded? 
  Pfeffer 
  (1900, 
  p. 
  515) 
  states 
  that 
  "the 
  mobilization 
  of 
  

   reserve 
  food 
  materials 
  is 
  regulated 
  by 
  the 
  amount 
  consumed;" 
  also 
  

   (p. 
  125), 
  " 
  when 
  growth 
  is 
  inhibited 
  the 
  consumption, 
  and 
  hence 
  also 
  

  

  