﻿384 
  JOURNAL 
  OF 
  THE 
  WASHINGTON 
  ACADEMY 
  OF 
  SCIENCES 
  VOL. 
  12, 
  NO. 
  16 
  

  

  Usually 
  soil 
  nematodes 
  go 
  as 
  deep 
  as 
  the 
  roots 
  of 
  plants 
  can 
  penetrate 
  

   and 
  therefore 
  the 
  depth 
  figures 
  recorded 
  in 
  publications 
  are 
  too 
  small. 
  

  

  Until 
  recently 
  nemas 
  have 
  been 
  almost 
  completely 
  disregarded 
  by 
  

   investigators 
  of 
  soil 
  economics, 
  and 
  especially 
  by 
  research 
  workers 
  in 
  

   soil 
  fertility. 
  

  

  If 
  we 
  wish 
  to 
  know 
  what 
  part 
  nematodes 
  play 
  in 
  the 
  economics 
  of 
  the 
  

   soil, 
  one 
  of 
  the 
  first 
  questions 
  to 
  be 
  answered 
  is 
  what 
  is 
  the 
  nature 
  of 
  

   their 
  food. 
  There 
  have 
  been 
  no 
  very 
  comprehensive 
  studies 
  made 
  of 
  

   this 
  question 
  up 
  to 
  the 
  present, 
  and 
  our 
  knowledge 
  is 
  based 
  mostly 
  on 
  

   only 
  occasional 
  observations. 
  The 
  results 
  of 
  these 
  show 
  that 
  some 
  

   forms 
  such 
  as 
  Rhabditis, 
  Cephalohus, 
  etc. 
  feed 
  on 
  decaying 
  matter, 
  

   that 
  is 
  on 
  the 
  contained 
  bacteria 
  or 
  bacterial 
  products 
  ; 
  others, 
  such 
  as 
  

   Tylenchus, 
  Heterodera, 
  Aphelenchits, 
  etc. 
  feed 
  on 
  plant 
  tissues 
  or 
  fluids; 
  

   others 
  such 
  as 
  Dorylaimus, 
  etc. 
  feed 
  probably 
  on 
  both 
  plants 
  and 
  ani- 
  

   mals; 
  and 
  still 
  others 
  such 
  as 
  Monoiichus 
  papillatits, 
  described 
  in 
  this 
  

   paper, 
  are 
  apparently 
  exclusively 
  predatory. 
  So 
  that 
  not 
  only 
  the 
  

   problem 
  of 
  combating 
  nematode 
  pests 
  in 
  soil 
  by 
  the 
  use 
  of 
  their 
  natural 
  

   enemies 
  will 
  be 
  attacked 
  by 
  investigations 
  along 
  this 
  line, 
  but 
  also 
  the 
  

   problem 
  of 
  soil 
  fertility 
  itself. 
  

  

  Today 
  we 
  know 
  that 
  soil 
  nematodes 
  play 
  a 
  very 
  important 
  role, 
  

  

  1. 
  As 
  consumers 
  and 
  destroyers 
  of 
  our 
  crops; 
  — 
  often 
  destroying 
  

   whole 
  fields, 
  but 
  much 
  oftener 
  decreasing 
  their 
  yield 
  in 
  a 
  less 
  per- 
  

   ceptible 
  degree. 
  

  

  2. 
  As 
  consumers 
  of, 
  and 
  as 
  important 
  workers 
  in 
  the 
  distribution 
  of 
  

   the 
  bacterial 
  flora 
  of 
  the 
  soil. 
  Their 
  activity 
  is 
  certainly 
  not 
  restricted 
  

   to 
  denitrifying 
  bacteria, 
  but 
  extends 
  to 
  nitrifying 
  forms 
  as 
  well. 
  A 
  

   closer 
  study 
  may 
  show 
  relations 
  of 
  very 
  great 
  importance. 
  They 
  carry 
  

   bacteria 
  and 
  fungus 
  spores 
  everywhere. 
  Wounds 
  on 
  roots 
  or 
  other 
  

   parts 
  of 
  plants 
  may 
  very 
  often 
  be 
  infected 
  by 
  bacterial 
  and 
  fungus 
  

   diseases 
  carried 
  by 
  these 
  nematodes. 
  (See 
  Metcalf 
  15.) 
  

  

  3. 
  As 
  having 
  relationships 
  with 
  fungi 
  upon 
  which 
  some 
  species 
  are 
  

   known 
  to 
  feed. 
  According 
  to 
  Zopf 
  fungi 
  on 
  the 
  other 
  hand 
  may 
  use 
  

   nematodes 
  as 
  prey. 
  

  

  4. 
  As 
  consumers 
  of 
  protozoa. 
  It 
  is 
  known 
  that 
  certain 
  fresh- 
  water 
  

   nemas 
  feed 
  specially 
  on 
  protozoa, 
  sometimes 
  apparently 
  on 
  a 
  single 
  

   species. 
  There 
  is 
  a 
  probability 
  that 
  some 
  soil 
  species 
  may 
  feed 
  in 
  a 
  

   similar 
  way, 
  and 
  further 
  investigations 
  may 
  enable 
  us 
  to 
  combat 
  plant 
  

   injurious 
  protozoa 
  by 
  the 
  use 
  of 
  these 
  nemas. 
  

  

  5. 
  As 
  furnishing 
  a 
  control 
  for 
  plant-injurious 
  nemas. 
  This 
  refers 
  to 
  

   the 
  work 
  of 
  predatory 
  nemas, 
  such 
  as 
  Mononchus 
  papillatus, 
  whose 
  

  

  