﻿230 
  ANNUAL 
  REPORT 
  SMITHSONIAN 
  INSTITUTION, 
  1922. 
  

  

  brook 
  near 
  by. 
  This 
  agrees 
  with 
  my 
  own 
  observations. 
  Size 
  is 
  far 
  

   from 
  a 
  final 
  indication 
  of 
  age. 
  The 
  General 
  Grant 
  tree, 
  which 
  has 
  

   no 
  running 
  water 
  near 
  it 
  and 
  is 
  the 
  largest 
  in 
  the 
  park 
  of 
  that 
  name, 
  

   has 
  a 
  burnt 
  area 
  on 
  one 
  side 
  in 
  which 
  the 
  outer 
  rings 
  are 
  exposed, 
  

   allowing 
  an 
  estimate 
  of 
  its 
  average 
  rate 
  of 
  recent 
  growth. 
  From 
  

   much 
  experience 
  with 
  the 
  way 
  the 
  sequoia 
  growth 
  is 
  influenced 
  by 
  

   age, 
  it 
  was 
  possible 
  to 
  assign 
  2,500 
  years 
  as 
  the 
  approximate 
  time 
  it 
  

   took 
  this 
  giant 
  to 
  reach 
  its 
  present 
  immense 
  diameter 
  of 
  close 
  to 
  30 
  

   feet. 
  But 
  about 
  3 
  miles 
  west 
  near 
  a 
  running 
  brook 
  is 
  a 
  stump 
  

   which 
  is 
  over 
  25 
  feet 
  in 
  diameter, 
  but 
  is 
  only 
  about 
  1,500 
  years 
  old. 
  

   That 
  is 
  the 
  effect 
  of 
  contact 
  with 
  an 
  unfailing 
  source 
  of 
  water. 
  

  

  Perhaps 
  the 
  most 
  general 
  characteristic 
  which 
  stands 
  out 
  in 
  the 
  

   different 
  groups 
  of 
  dry-climate 
  trees 
  is 
  a 
  close 
  relationship 
  of 
  this 
  

   kind 
  between 
  the 
  topography 
  and 
  the 
  growth 
  produced. 
  For 
  that 
  

   reason, 
  I 
  have 
  visited 
  the 
  site 
  of 
  every 
  dry-climate 
  group 
  and 
  indeed 
  

   have 
  examined 
  the 
  stumps 
  of 
  almost 
  every 
  tree 
  in 
  my 
  collection. 
  

  

  It 
  was 
  found 
  that 
  dry-climate 
  trees 
  which 
  grew 
  in 
  basins 
  with 
  a 
  

   large 
  and 
  constant 
  water 
  supply, 
  and 
  this 
  refers 
  especially 
  to 
  the 
  

   sequoias, 
  usually 
  produced 
  rings 
  without 
  much 
  change 
  in 
  size 
  from 
  

   year 
  to 
  year. 
  This 
  character 
  of 
  ring 
  is 
  called 
  "complacent." 
  The 
  

   opposite 
  character 
  is 
  the 
  " 
  sensitive 
  " 
  ring 
  where 
  a 
  decided 
  variation 
  

   is 
  shown 
  from 
  year 
  to 
  year. 
  Sensitive 
  trees 
  grow 
  on 
  the 
  higher 
  eleva- 
  

   tions 
  where 
  the 
  water 
  supply 
  is 
  not 
  reliable 
  and 
  the 
  tree 
  must 
  de- 
  

   pend 
  almost 
  entirely 
  on 
  the 
  precipitation 
  during 
  each 
  year. 
  Such 
  

   trees 
  grow 
  near 
  the 
  tops 
  of 
  ridges 
  or 
  are 
  otherwise 
  separated 
  from 
  

   any 
  collection 
  of 
  water 
  in 
  the 
  ground. 
  In 
  case 
  of 
  the 
  basin 
  trees, 
  

   one 
  could 
  be 
  sure 
  that 
  a 
  ring 
  was 
  produced 
  every 
  year, 
  but 
  owing 
  

   to 
  the 
  lack 
  of 
  individuality 
  in 
  the 
  rings 
  for 
  certain 
  years, 
  it 
  was 
  

   difficult 
  to 
  compare 
  trees 
  together 
  and 
  produce 
  reliable 
  data. 
  In 
  

   case 
  of 
  the 
  sensitive 
  tree 
  growing 
  in 
  the 
  uplands 
  there 
  was 
  so 
  much 
  

   individuality 
  in 
  the 
  rings 
  that 
  nearly 
  all 
  of 
  the 
  trees 
  could 
  be 
  

   dated 
  with 
  perfect 
  reliability, 
  but 
  in 
  extreme 
  cases 
  the 
  omission 
  

   of 
  rings 
  in 
  a 
  number 
  of 
  trees 
  required 
  special 
  study. 
  Of 
  course, 
  

   these 
  cases 
  were 
  easily 
  settled 
  by 
  comparison 
  with 
  other 
  trees 
  grow- 
  

   ing 
  in 
  intermediate 
  localities. 
  

  

  Trees 
  growing 
  in 
  the 
  dry 
  climate 
  of 
  Arizona 
  at 
  an 
  altitude 
  where 
  

   they 
  have 
  the 
  utmost 
  difficulty 
  in 
  getting 
  water 
  to 
  prolong 
  life 
  be- 
  

   come 
  extraordinarily 
  sensitive. 
  In 
  the 
  same 
  tree 
  one 
  finds 
  some 
  

   rings 
  several 
  millimeters 
  across 
  and 
  others 
  microscopic 
  in 
  size 
  or 
  

   even 
  absent. 
  

  

  In 
  order 
  to 
  express 
  this 
  different 
  quality 
  in 
  the 
  trees 
  a 
  criterion 
  

   called 
  mean 
  sensitivity 
  is 
  now 
  under 
  investigation. 
  It 
  may 
  be 
  de- 
  

   fined 
  as 
  the 
  difference 
  between 
  two 
  successive 
  rings 
  divided 
  by 
  their 
  

   mean. 
  Such 
  quotients 
  are 
  averaged 
  over 
  each 
  decade 
  or 
  other 
  period 
  

  

  