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  ANNUAL 
  REPORT 
  SMITHSONIAN 
  INSTITUTION, 
  1943 
  

  

  SOUTHWESTERN 
  TROPICAL 
  YUNNAN 
  

  

  The 
  southwestern 
  part 
  of 
  Yunnan 
  adjacent 
  to 
  Burma 
  is 
  under 
  the 
  

   influence 
  of 
  the 
  monsoon 
  winds 
  which 
  in 
  summer 
  flow 
  from 
  the 
  Bay 
  

   of 
  Bengal 
  laden 
  with 
  moisture. 
  The 
  lower 
  portions 
  of 
  the 
  great 
  

   parallel 
  gorges, 
  which 
  are 
  such 
  a 
  prominent 
  feature 
  of 
  western 
  Yun- 
  

   nan, 
  lie 
  under 
  the 
  influence 
  of 
  these 
  winds 
  and 
  are 
  filled 
  with 
  luxuri- 
  

   ant 
  rain-forest 
  vegetation. 
  Here 
  most 
  of 
  the 
  trees 
  are 
  evergreen, 
  

   and 
  the 
  jungles 
  are 
  filled 
  with 
  lianas, 
  palms, 
  tropical 
  nettles, 
  and 
  

   other 
  characteristic 
  plants 
  of 
  the 
  dense 
  rain 
  forests. 
  This 
  floristic 
  

   region 
  of 
  China 
  is 
  only 
  an 
  extension 
  of 
  that 
  of 
  Burma 
  and 
  Siam. 
  

   Many 
  of 
  the 
  very 
  numerous 
  species 
  of 
  plants 
  occurring 
  here 
  are 
  Indo- 
  

   Malayan 
  or 
  are 
  characteristic 
  of 
  tropical 
  India. 
  As 
  in 
  other 
  tropical 
  

   rain 
  forests, 
  malaria 
  is 
  common 
  and 
  conditions 
  are 
  unfavorable 
  for 
  

   human 
  habitation. 
  This 
  diffculty 
  is 
  overcome 
  in 
  some 
  of 
  the 
  gorges 
  

   by 
  building 
  the 
  villages 
  high 
  up 
  on 
  the 
  sides, 
  whence 
  the 
  people 
  

   descend 
  to 
  the 
  fertile 
  river 
  bottoms 
  to 
  till 
  their 
  crops. 
  

  

  Southern 
  Yunnan 
  also 
  has 
  a 
  highly 
  tropical 
  vegetation 
  with 
  many 
  

   species 
  of 
  plants 
  which 
  likewise 
  occur 
  in 
  Hainan 
  and 
  elsewhere 
  in 
  

   southeastern 
  China, 
  but 
  with 
  a 
  gap 
  between. 
  There 
  is, 
  however, 
  in 
  

   the 
  valley 
  of 
  the 
  Ked 
  River 
  and 
  adjacent 
  streams 
  a 
  dry 
  area 
  of 
  limited 
  

   extent 
  due 
  to 
  local 
  variations 
  in 
  climate. 
  

  

  THE 
  HIGHLANDS 
  OF 
  WESTERN 
  CHINA 
  

  

  The 
  western 
  and 
  northwestern 
  portion 
  of 
  Yunnan 
  is 
  botanically 
  

   more 
  or 
  less 
  distinct 
  from 
  the 
  great 
  dissected 
  plateau 
  to 
  the 
  east 
  and 
  

   the 
  monsoon-drenched 
  mountains 
  and 
  lower 
  ends 
  of 
  the 
  gorges 
  to 
  

   the 
  south. 
  In 
  these 
  deep 
  gorges 
  flow 
  the 
  great 
  rivers 
  which 
  arise 
  

   on 
  the 
  Tibetan 
  plateau 
  and 
  cut 
  across 
  the 
  eastward 
  and 
  northeast- 
  

   ward 
  extension 
  of 
  the 
  highest 
  mountains 
  of 
  the 
  world, 
  the 
  Himalayan 
  

   Range. 
  Originally 
  these 
  mountains 
  extended 
  in 
  an 
  east-west 
  direc- 
  

   tion, 
  but 
  their 
  deep 
  intersection 
  by 
  southward-flowing 
  streams 
  has 
  left 
  

   the 
  intervening 
  ridges 
  stretching 
  north 
  and 
  south. 
  The 
  original 
  

   mountain 
  peaks 
  tower 
  up 
  to 
  over 
  20,000 
  feet, 
  well 
  up 
  into 
  the 
  regions 
  

   of 
  perpetual 
  snow. 
  It 
  is 
  obvious 
  that 
  this 
  tremendous 
  range 
  in 
  alti- 
  

   tude 
  and 
  the 
  extremely 
  rugged 
  character 
  of 
  the 
  land 
  would 
  greatly 
  

   affect 
  the 
  type 
  of 
  vegetation 
  found 
  in 
  the 
  region. 
  

  

  When 
  the 
  moisture-laden 
  monsoon 
  winds 
  from 
  the 
  southwest 
  are 
  

   forced 
  to 
  rise 
  up 
  the 
  slopes 
  of 
  these 
  mountains 
  they 
  lose 
  their 
  load 
  

   and 
  are 
  dissipated. 
  Hence 
  the 
  vegetation 
  in 
  this 
  region 
  is 
  less 
  lux- 
  

   uriant 
  than 
  that 
  farther 
  south. 
  Another 
  meteorological 
  phenomenon 
  

   that 
  occurs 
  in 
  the 
  gorges 
  results 
  in 
  very 
  arid 
  conditions. 
  During 
  the 
  

   day 
  the 
  sun 
  heats 
  the 
  air 
  in 
  these 
  closed-in 
  canyons 
  to 
  a 
  temperature 
  

   much 
  above 
  that 
  in 
  the 
  side 
  canyons 
  and 
  on 
  the 
  surrounding 
  moun- 
  

  

  