﻿PLANTS 
  OF 
  CHINA 
  — 
  WALKER 
  347 
  

  

  tains. 
  About 
  the 
  middle 
  of 
  the 
  afternoon 
  this 
  heated 
  air 
  suddenly 
  

   starts 
  to 
  rise 
  and 
  creates 
  such 
  a 
  current 
  that 
  any 
  attempts 
  of 
  moisture- 
  

   laden 
  monsoon 
  winds 
  from 
  the 
  southwest 
  to 
  penetrate 
  the 
  area 
  are 
  

   completely 
  thwarted. 
  This 
  dry 
  area 
  occurs 
  in 
  the 
  valleys 
  of 
  the 
  Sal- 
  

   ween, 
  Mekong 
  (pi. 
  7, 
  fig. 
  1), 
  and 
  Yangtze 
  Rivers. 
  On 
  the 
  Salween 
  

   it 
  begins 
  at 
  about 
  the 
  28th 
  parallel 
  but 
  farther 
  south 
  on 
  the 
  other 
  riv- 
  

   ers. 
  On 
  the 
  Yangtze 
  it 
  includes 
  the 
  gorges 
  around 
  the 
  great 
  bend 
  

   north 
  of 
  Likiang. 
  

  

  Thus 
  only 
  drought-resistant 
  stunted 
  shrubs 
  and 
  moisture-holding 
  

   herbs 
  can 
  survive 
  here 
  and 
  the 
  vegetation 
  in 
  part 
  is 
  related 
  to 
  that 
  of 
  

   Central 
  Asia. 
  A 
  strange 
  exotic 
  is 
  an 
  American 
  cactus 
  (Opuntia) 
  

   which 
  somehow 
  reached 
  this 
  out-of-the-way 
  land 
  and 
  found 
  con- 
  

   ditions 
  favorable 
  to 
  its 
  growth 
  and 
  survival. 
  Its 
  seeds 
  and 
  fruits 
  

   are 
  eaten 
  by 
  men, 
  beasts, 
  and 
  birds. 
  How 
  it 
  arrived 
  is 
  quite 
  un- 
  

   known. 
  Possibly 
  it 
  was 
  brought 
  by 
  some 
  missionary 
  long 
  ago 
  or 
  

   possibly 
  it 
  came 
  with 
  some 
  caravan 
  from 
  the 
  Near 
  East 
  where 
  it 
  was 
  

   introduced 
  soon 
  after 
  the 
  discovery 
  of 
  America. 
  

  

  Higher 
  up 
  on 
  the 
  mountains 
  occur 
  great 
  forests 
  of 
  deciduous 
  trees 
  

   of 
  various 
  kinds, 
  then 
  conifers 
  in 
  zones 
  (pi. 
  6), 
  then 
  rhododendron 
  

   thickets, 
  and 
  finally 
  alpine 
  formations 
  of 
  various 
  kinds, 
  especially 
  the 
  

   gorgeous 
  alpine 
  meadows. 
  Here 
  is 
  found 
  the 
  rich 
  vegetation 
  so 
  

   eagerly 
  sought 
  for 
  by 
  plant 
  explorers 
  in 
  search 
  of 
  ornamentals 
  for 
  

   western 
  gardens, 
  especially 
  rock 
  gardens 
  (pi. 
  5, 
  fig. 
  1). 
  This 
  is 
  the 
  

   plant-lover's 
  paradise, 
  for 
  from 
  this 
  varied 
  region 
  have 
  come 
  many 
  

   of 
  our 
  most 
  exquisite 
  rhododendrons, 
  primulas, 
  poppies, 
  larkspurs, 
  

   and 
  other 
  garden 
  favorites. 
  Here 
  occur 
  vast 
  forests, 
  mostly 
  as 
  yet 
  

   unexploited, 
  a 
  future 
  storehouse 
  safe 
  from 
  the 
  ax 
  until 
  railroads 
  

   and 
  roads 
  have 
  opened 
  it 
  up. 
  

  

  The 
  area 
  extends 
  northward 
  from 
  Yunnan 
  through 
  eastern 
  Sikang 
  

   and 
  Tsinghai 
  to 
  western 
  Kansu. 
  It 
  is 
  peopled 
  largely 
  by 
  Tibetans 
  

   and 
  has 
  been 
  called 
  Tibetan 
  China. 
  On 
  the 
  east 
  it 
  merges 
  with 
  the 
  

   more 
  temperate 
  or 
  even 
  subtropical 
  vegetation 
  of 
  Szechwan 
  and 
  on 
  

   the 
  west 
  with 
  the 
  grasslands 
  of 
  Tibet. 
  

  

  In 
  respect 
  to 
  affinities 
  this 
  rich 
  flora 
  contains 
  many 
  elements 
  of 
  

   the 
  Himalayan 
  flora 
  of 
  northern 
  India, 
  in 
  contrast 
  with 
  that 
  of 
  

   tropical 
  Yunnan, 
  which 
  is 
  largely 
  Indo-Malayan. 
  It 
  contains 
  also 
  

   a 
  large 
  number 
  of 
  endemics 
  as 
  well 
  as 
  elements 
  of 
  the 
  flora 
  of 
  middle 
  

   China. 
  Yunnan 
  as 
  a 
  whole 
  has 
  the 
  richest 
  flora 
  of 
  any 
  of 
  the 
  18 
  

   provinces 
  of 
  China, 
  having 
  over 
  6,300 
  species. 
  This 
  is 
  not 
  surpris- 
  

   ing 
  in 
  view 
  of 
  the 
  great 
  diversity 
  of 
  climatic 
  and 
  physiographic 
  con- 
  

   ditions, 
  the 
  proximity 
  of 
  a 
  great 
  variety 
  of 
  floras 
  of 
  different 
  

   composition 
  and 
  origin, 
  and 
  the 
  long 
  uninterrupted 
  geological 
  history 
  

   of 
  the 
  larger 
  part 
  of 
  the 
  province. 
  

  

  