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  diseases 
  of 
  citrus 
  fruits, 
  so 
  you 
  must 
  not 
  be 
  surprised 
  that 
  we 
  cannot 
  

   put 
  a 
  group 
  of 
  men 
  on 
  this 
  problem 
  and 
  study 
  it 
  as 
  it 
  should 
  be 
  

   studied. 
  It 
  is 
  a 
  question 
  of 
  men 
  and 
  means. 
  

  

  Perhaps 
  now 
  some 
  general 
  information 
  might 
  be 
  of 
  interest 
  and 
  

   set 
  you 
  to 
  thinking. 
  

  

  In 
  the. 
  first 
  place 
  in 
  every 
  disease 
  problem, 
  conspicuously 
  so 
  with 
  

   our 
  fruit 
  and 
  nut 
  diseases, 
  there 
  are 
  two 
  main 
  classes 
  of 
  plants 
  to 
  be 
  

   considered, 
  our 
  native 
  plants 
  and 
  the 
  foreign 
  plants. 
  The 
  pathol- 
  

   ogist 
  is 
  always 
  looking 
  to 
  the 
  native 
  origin 
  of 
  a 
  plant 
  in 
  studying 
  its 
  

   adaptation 
  to 
  the 
  environment 
  in 
  which 
  it 
  is 
  attempted 
  to 
  be 
  grown. 
  

   A 
  foreign 
  plant 
  may 
  not 
  necessarily 
  be 
  unadapted 
  to 
  another 
  

   locality. 
  The 
  vinifera 
  grape 
  is 
  thoroughly 
  adapted 
  to 
  California 
  

   and 
  to 
  much 
  of 
  the 
  Pacific 
  slope 
  beyond 
  the 
  Rocky 
  Mountains, 
  but 
  

   you 
  know 
  the 
  vinifera 
  grape 
  has 
  a 
  hard 
  struggle 
  in 
  other 
  parts 
  of 
  

   the 
  United 
  States. 
  This 
  is 
  not 
  only 
  a 
  pathological 
  problem 
  but 
  a 
  

   physiological 
  one. 
  It 
  cannot 
  stand 
  a 
  soaking 
  rain 
  for 
  two 
  weeks 
  at 
  

   a 
  time 
  ; 
  it 
  cannot 
  stand 
  so 
  much 
  water 
  and 
  humidity 
  but 
  it 
  wants 
  

   dry, 
  hot 
  sunshine 
  continuously 
  from 
  the 
  time 
  it 
  puts 
  out 
  its 
  leaves 
  

   in 
  the 
  spring. 
  

  

  Another 
  phase 
  still 
  more 
  interesting 
  is 
  the 
  question 
  of 
  foreign 
  

   parasites. 
  Many 
  of 
  the 
  worst 
  diseases 
  with 
  which 
  we 
  have 
  to 
  con- 
  

   tend 
  are 
  either 
  native 
  diseases 
  attacking 
  introduced 
  plants, 
  or 
  

   foreign 
  diseases 
  attacking 
  native 
  plants. 
  I 
  will 
  take 
  that 
  up 
  in 
  

   detail. 
  Nature 
  has 
  fought 
  the 
  battle 
  all 
  out 
  with 
  the 
  native 
  para- 
  

   sites 
  -against 
  the 
  native 
  host 
  plants, 
  so 
  we 
  don't 
  have 
  to 
  do 
  it. 
  It's 
  

   a 
  case 
  of 
  the 
  survival 
  of 
  the 
  fittest. 
  They 
  have 
  won, 
  so 
  when 
  we 
  are 
  

   dealing 
  with 
  native 
  plants 
  against 
  our 
  native 
  diseases, 
  we 
  have 
  a 
  

   condition 
  that 
  has 
  been 
  fought 
  out 
  in 
  nature 
  for 
  nobody 
  knows 
  

   how 
  many 
  thousand 
  years. 
  The 
  result 
  is 
  that 
  unless 
  we 
  disturb 
  the 
  

   balance 
  too 
  much 
  by 
  cultivating 
  great 
  orchards 
  of 
  a 
  thing 
  that 
  has 
  

   been 
  grown 
  as 
  scattered 
  individuals, 
  or 
  overforcing 
  it 
  or 
  selecting 
  

   and 
  breeding 
  towards 
  larger 
  fruit 
  without 
  any 
  regard 
  to 
  foliage 
  

   and 
  other 
  characters 
  we 
  can 
  go 
  ahead 
  with 
  our 
  breeding 
  and 
  selec- 
  

   tion 
  and 
  cultivation 
  and 
  trust 
  nature 
  to 
  keep 
  the 
  balance 
  to 
  some 
  

   extent. 
  We 
  have 
  this 
  natural 
  balance 
  in 
  our 
  favor 
  in 
  dealing 
  with 
  

   the 
  problem 
  of 
  cultivating 
  native 
  plants. 
  As 
  an 
  example 
  take 
  the 
  

   pear 
  and 
  apple 
  blight. 
  The 
  pear 
  blight 
  problem 
  is 
  one 
  in 
  which 
  a 
  

   native 
  parasite 
  on 
  wild 
  crab 
  apples, 
  which 
  occasionally 
  kills 
  a 
  few 
  

   twigs 
  here 
  and 
  there, 
  attacks 
  the 
  juicy, 
  tender, 
  susceptible, 
  intro- 
  

   duced 
  European 
  pear 
  and 
  makes 
  a 
  very 
  serious 
  disease. 
  It 
  is 
  a 
  

   fight 
  indeed 
  to 
  grow 
  it 
  in 
  so 
  much 
  of 
  the 
  country 
  that 
  pear 
  culture 
  

   has 
  been 
  very 
  largely 
  suppressed 
  over 
  the 
  eastern 
  half 
  of 
  the 
  United 
  

  

  