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  ANNUAL 
  REPORT 
  SMITHSONIAN 
  INSTITUTION, 
  1943 
  

  

  the 
  plants 
  best 
  adapted 
  to 
  the 
  conditions 
  under 
  which 
  he 
  must 
  oper- 
  

   ate. 
  That 
  American 
  planters 
  in 
  the 
  early 
  days 
  gave 
  their 
  attention 
  

   so 
  exclusively 
  to 
  Castilla, 
  and 
  planters 
  in 
  the 
  East 
  Indies 
  to 
  the 
  Para 
  

   rubber, 
  was 
  not 
  the 
  result 
  of 
  any 
  demonstration 
  of 
  the 
  cultural 
  su- 
  

   periority 
  of 
  one 
  tree 
  or 
  the 
  other, 
  but 
  of 
  becoming 
  interested 
  in 
  the 
  

   possibilities 
  of 
  the 
  tree 
  they 
  had 
  at 
  hand. 
  The 
  desirability 
  of 
  many 
  

   other 
  species 
  that 
  have 
  been 
  reported 
  as 
  promising 
  remains 
  to 
  be 
  

   determined. 
  

  

  It 
  is 
  not 
  to 
  be 
  expected 
  that 
  any 
  one 
  species 
  will 
  be 
  found 
  to 
  have 
  

   a 
  sufficiently 
  superior 
  value 
  under 
  all 
  conditions 
  to 
  warrant 
  its 
  being 
  

   planted 
  to 
  the 
  exclusion 
  of 
  all 
  others. 
  Rubber, 
  like 
  starch, 
  is 
  pro- 
  

   duced 
  in 
  nature 
  in 
  many 
  different 
  environments 
  ranging 
  from 
  deserts 
  

   to 
  swamps. 
  The 
  number 
  of 
  cultivated 
  rubber 
  plants 
  will 
  probably 
  

   never 
  equal 
  that 
  of 
  the 
  starchy 
  cereals 
  and 
  root 
  crops 
  ; 
  but 
  there 
  is 
  the 
  

   same 
  practical 
  reason 
  why 
  the 
  cultural 
  requirements, 
  hardiness, 
  vigor, 
  

   and 
  productiveness 
  of 
  the 
  different 
  rubber 
  plants 
  should 
  be 
  consid- 
  

   ered 
  — 
  not 
  merely 
  those 
  of 
  the 
  distinct 
  genera 
  and 
  species, 
  but 
  also 
  

   those 
  of 
  the 
  varieties 
  of 
  races 
  into 
  which 
  each 
  species 
  will 
  be 
  found 
  

   divisible 
  by 
  cultural 
  selection. 
  The 
  cultural 
  characters 
  or 
  adaptive 
  

   differences 
  of 
  behavior 
  under 
  varied 
  conditions 
  are 
  as 
  important 
  as 
  

   differences 
  in 
  percentage 
  of 
  rubber, 
  or 
  even 
  in 
  quality 
  of 
  rubber, 
  in 
  

   determining 
  whether 
  production 
  is 
  practically 
  feasible 
  in 
  competition 
  

   with 
  other 
  crops. 
  The 
  adaptive 
  ability 
  of 
  a 
  tree 
  or 
  plant 
  to 
  grow 
  

   readily 
  on 
  an 
  extensive 
  scale 
  and 
  produce 
  abundantly 
  under 
  condi- 
  

   tions 
  that 
  can 
  be 
  provided, 
  is 
  a 
  basic 
  requirement. 
  

  

  REASONS 
  FOR 
  PREFERRING 
  TREE 
  CROPS 
  

  

  Among 
  the 
  factors 
  to 
  be 
  recognized 
  in 
  rubber 
  production 
  are 
  the 
  

   general 
  advantages 
  of 
  tree 
  crops 
  over 
  field 
  crops, 
  especially 
  in 
  tropical 
  

   countries, 
  in 
  requiring 
  less 
  labor 
  and 
  affording 
  greater 
  protection 
  of 
  

   the 
  soil 
  against 
  erosion. 
  Rubber 
  plants 
  that 
  can 
  be 
  grown 
  as 
  annuals 
  

   or 
  biennials 
  in 
  northern 
  countries 
  may 
  be 
  valuod 
  as 
  insurance 
  against 
  

   emergencies 
  without 
  being 
  expected 
  to 
  compete 
  in 
  normal 
  production 
  

   with 
  rubber 
  produced 
  from 
  tropical 
  tree 
  crops. 
  The 
  costs 
  of 
  clear- 
  

   ing 
  the 
  land 
  and 
  weeding 
  the 
  crops 
  are 
  among 
  the 
  principal 
  items 
  

   of 
  expense 
  in 
  tropical 
  undertakings, 
  although 
  it 
  is 
  now 
  recognized 
  

   that 
  these 
  cultural 
  activities 
  often 
  lead 
  to 
  rapid 
  decline 
  of 
  soil 
  fer- 
  

   tility 
  through 
  surface 
  erosion. 
  The 
  only 
  permanent 
  agricultures 
  

   are 
  those 
  that 
  do 
  not 
  involve 
  the 
  working 
  of 
  the 
  soil. 
  Denudation 
  

   of 
  the 
  land 
  through 
  continued 
  cultivation 
  is 
  now 
  being 
  recognized 
  as 
  

   a 
  limiting 
  factor 
  of 
  agriculture 
  in 
  many 
  tropical 
  regions. 
  

  

  Vast 
  areas 
  in 
  the 
  Tropics 
  have 
  the 
  status 
  of 
  waste 
  lands, 
  more 
  or 
  

   less 
  denuded 
  by 
  previous 
  cultivation 
  and 
  burning, 
  and 
  lacking 
  the 
  

   surface 
  layer 
  of 
  fertile 
  soil, 
  which 
  may 
  be 
  formed 
  again 
  if 
  forest 
  con- 
  

  

  