﻿PLANT 
  INDUSTRIES 
  323 
  

  

  a 
  crop. 
  1 
  It 
  now 
  seems 
  probable 
  that 
  certain 
  drought-resisting 
  

   plants, 
  as 
  some 
  kinds 
  of 
  wheat, 
  2 
  will 
  make 
  it 
  possible 
  to 
  use 
  soils 
  

   which 
  have 
  not 
  been 
  usable 
  because 
  of 
  inadequate 
  moisture. 
  

  

  In 
  regions 
  where 
  available 
  water 
  supplies 
  exist, 
  irrigation 
  is 
  

   practicable. 
  Between 
  15,000,000 
  and 
  20,000,000 
  acres 
  of 
  land 
  

   are 
  said 
  to 
  be 
  under 
  irrigation 
  in 
  the 
  United 
  States, 
  but 
  this 
  

   area 
  is 
  small 
  compared 
  with 
  the 
  large 
  extent 
  of 
  our 
  so-called 
  

   desert 
  lands, 
  which 
  only 
  need 
  water 
  and 
  proper 
  cultivation 
  to 
  

   make 
  them 
  highly 
  productive. 
  

  

  304. 
  Effect 
  of 
  living 
  things 
  in 
  the 
  soil. 
  3 
  Microscopic 
  plants 
  

   and 
  animals 
  of 
  many 
  kinds 
  and 
  in 
  great 
  numbers 
  live 
  upon 
  

   one 
  another, 
  upon 
  plant 
  roots, 
  or 
  upon 
  dead 
  organic 
  matter 
  hi 
  

   the 
  soil. 
  The 
  roots 
  of 
  living 
  plants, 
  the 
  molds, 
  and 
  the 
  burrow- 
  

   ing 
  animals, 
  such 
  as 
  the 
  larvse 
  of 
  insects 
  and 
  the 
  earthworm, 
  

   constantly 
  take 
  from, 
  add 
  to, 
  or 
  otherwise 
  change 
  the 
  soil. 
  

   Earthworms 
  eat 
  their 
  way 
  through 
  it, 
  and 
  as 
  they 
  do 
  so 
  they 
  

   make 
  it 
  more 
  porous 
  and 
  excrete 
  materials 
  that 
  add 
  to 
  the 
  

   soil's 
  available 
  organic 
  matter. 
  Certain 
  groups 
  of 
  soil 
  bacteria 
  

   have 
  already 
  been 
  discussed 
  (sect. 
  191). 
  The 
  living 
  things 
  of 
  

   the 
  soil 
  may 
  be 
  said 
  to 
  constitute 
  an 
  extensive 
  and 
  intricate 
  

   group 
  of 
  plants 
  and 
  animals 
  living 
  close 
  together 
  and 
  greatly 
  

   affecting 
  the 
  nature 
  of 
  the 
  material 
  in 
  which 
  they 
  live. 
  Some 
  

   of 
  the 
  products 
  of 
  the 
  soil 
  inhabitants 
  are 
  helpful 
  to 
  agricultural 
  

   plants 
  and 
  some 
  are 
  harmful. 
  

  

  305. 
  Quality 
  of 
  soil 
  and 
  growth 
  of 
  plants. 
  A 
  comparison 
  of 
  

   plants 
  of 
  the 
  same 
  kind 
  that 
  have 
  grown 
  in 
  different 
  regions 
  

   readily 
  shows 
  that 
  soils 
  differ 
  widely 
  in 
  their 
  ability 
  to 
  sup- 
  

   port 
  vegetation. 
  Even 
  the 
  different 
  parts 
  of 
  the 
  root 
  system 
  

   of 
  one 
  plant 
  illustrate 
  this 
  fact 
  (fig. 
  238). 
  Soils 
  that 
  are 
  at 
  

   one 
  time 
  fertile 
  may 
  lose 
  that 
  fertility, 
  as 
  may 
  be 
  seen 
  in 
  any 
  

   farming 
  region. 
  Many 
  studies 
  are 
  being 
  made, 
  to 
  determine 
  how 
  

   fertility 
  is 
  lost 
  and 
  what 
  will 
  restore 
  it, 
  and 
  while 
  the 
  question 
  

  

  Farming 
  in 
  Relation 
  to 
  Rainfall 
  and 
  Evaporation," 
  Bulletin 
  188, 
  

   Bureau 
  of 
  Plant 
  Industry, 
  U.S. 
  Dept. 
  Agr., 
  1913. 
  

  

  2 
  Native 
  wheat 
  which 
  is 
  thought 
  to 
  be 
  primitive 
  has 
  been 
  found 
  growing 
  

   wild 
  in 
  arid 
  districts 
  in 
  Palestine. 
  

  

  8 
  See 
  Marshall, 
  Microbiology, 
  P. 
  Blakiston's 
  Sou 
  & 
  Co., 
  Philadelphia. 
  

  

  