﻿348 
  ANNUAL 
  REPORT 
  SMITHSONIAN 
  INSTITUTION, 
  194 
  3 
  

  

  Far 
  back 
  in 
  geological 
  history, 
  in 
  the 
  Oligocene 
  period, 
  Eurasia 
  

   was 
  divided 
  by 
  the 
  Tethys 
  Sea, 
  which 
  occupied 
  about 
  the 
  present 
  

   location 
  of 
  Burma, 
  Assam, 
  and 
  Tibet 
  and 
  separated 
  China 
  from 
  

   India. 
  Asia 
  was 
  a 
  continent 
  of 
  undulating 
  wooded 
  lowlands 
  without 
  

   high 
  mountains. 
  The 
  flora 
  was 
  probably 
  fairly 
  uniform. 
  Later 
  

   mountains 
  were 
  formed 
  which 
  upset 
  the 
  climate 
  and 
  brought 
  about 
  

   a 
  diversified 
  flora. 
  Finally 
  the 
  Himalayan 
  uplift 
  occurred, 
  which 
  

   eliminated 
  the 
  Tethys 
  Sea 
  and 
  replaced 
  it 
  with 
  the 
  world's 
  highest 
  

   mountains, 
  through 
  which 
  the 
  rivers 
  from 
  the 
  uplifted 
  Tibetan 
  pla- 
  

   teau 
  cut 
  transverse 
  courses. 
  In 
  the 
  succeeding 
  Pleistocene 
  period 
  

   huge 
  glaciers 
  developed 
  in 
  these 
  mountains 
  and 
  spread 
  out 
  north- 
  

   ward 
  over 
  the 
  southern 
  half 
  of 
  Tibet 
  and 
  east 
  and 
  south 
  over 
  western 
  

   Yunnan. 
  Thus 
  the 
  plants 
  of 
  these 
  ice-covered 
  parts 
  were 
  wiped 
  out, 
  

   but, 
  because 
  of 
  the 
  limited 
  spread 
  of 
  the 
  glaciers 
  eastward, 
  the 
  vegeta- 
  

   tion 
  of 
  central 
  and 
  eastern 
  Yunnan 
  remained. 
  It 
  may 
  have 
  been 
  

   altered 
  and 
  forced 
  southward 
  but 
  was 
  not 
  destroyed. 
  When 
  the 
  

   glaciers 
  receded, 
  this 
  altered 
  vegetation 
  spread 
  back 
  into 
  the 
  released 
  

   western 
  part 
  of 
  the 
  province, 
  and 
  the 
  plants 
  of 
  Indo-Malaya 
  spread 
  

   northward 
  again. 
  At 
  the 
  same 
  time 
  conditions 
  were 
  favorable 
  for 
  

   the 
  flora 
  developed 
  in 
  northern 
  India 
  to 
  invade 
  this 
  territory. 
  Hence, 
  

   the 
  Yunnan 
  flora 
  today 
  contains 
  elements 
  from 
  the 
  diverse 
  floral 
  

   regions 
  round 
  about, 
  as 
  well 
  as 
  remnants 
  of 
  the 
  early 
  flora 
  developed 
  

   in 
  the 
  province 
  in 
  earlier 
  geological 
  times. 
  The 
  lack 
  of 
  extensive 
  

   glaciation 
  in 
  north 
  China, 
  such 
  as 
  occurred 
  in 
  Europe 
  and 
  northern 
  

   North 
  America, 
  accounts 
  in 
  part 
  for 
  the 
  richness 
  of 
  the 
  flora 
  of 
  China 
  

   as 
  a 
  whole 
  in 
  comparison 
  with 
  that 
  of 
  the 
  heavily 
  glaciated 
  continents. 
  

  

  THE 
  GRASSLANDS 
  OF 
  EASTERN 
  TTBET 
  

  

  The 
  grasslands 
  of 
  eastern 
  Tibet 
  lie 
  in 
  the 
  new 
  provinces 
  of 
  Sikang 
  

   and 
  Tsinghai 
  west 
  of 
  the 
  great 
  mountain 
  ranges 
  of 
  western 
  China 
  

   and 
  extend 
  somewhat 
  into 
  western 
  Kansu 
  Province 
  (pi. 
  7, 
  fig. 
  2). 
  

   These 
  lands 
  are 
  the 
  home 
  of 
  the 
  Tibetan 
  nomads 
  where 
  flocks 
  of 
  yak 
  

   are 
  herded 
  and 
  the 
  people 
  live 
  in 
  yerts 
  or 
  felt 
  tents. 
  The 
  vegetation 
  

   is 
  almost 
  entirely 
  composed 
  of 
  grasses 
  and 
  grasslike 
  plants, 
  with 
  

   many 
  herbs 
  remarkable 
  for 
  their 
  ability 
  to 
  burst 
  forth 
  early 
  in 
  the 
  

   short 
  growing 
  season, 
  cover 
  the 
  landscape 
  with 
  a 
  riot 
  of 
  gorgeous 
  

   color, 
  and 
  quickly 
  ripen 
  and 
  shed 
  their 
  seeds 
  before 
  the 
  early 
  winter 
  

   forces 
  them 
  into 
  dormancy 
  again. 
  Shrubs 
  and 
  trees 
  are 
  few 
  or 
  

   wanting 
  on 
  the 
  uplands, 
  but 
  exist 
  in 
  the 
  sheltered 
  valleys 
  and 
  in 
  belts 
  

   on 
  the 
  mountains, 
  where 
  the 
  clouds 
  are 
  forced 
  to 
  drop 
  more 
  moisture. 
  

  

  The 
  vegetation 
  of 
  these 
  grasslands 
  is 
  essentially 
  central 
  Asiatic 
  and 
  

   alpine, 
  and 
  the 
  few 
  woody 
  plants 
  and 
  trees 
  are 
  largely 
  of 
  northern 
  

   affinities. 
  

  

  