﻿ANNUAL 
  RINGS 
  OF 
  TREES 
  — 
  DOUGLASS. 
  227 
  

  

  ful 
  search 
  that 
  they 
  often 
  increase 
  the 
  feeling 
  of 
  certainty 
  in 
  the 
  

   dating 
  of 
  rings. 
  

  

  Missing 
  rings 
  occur 
  when 
  autumn 
  rings 
  merge 
  together 
  in 
  the 
  

   absence 
  of 
  any 
  spring 
  growth. 
  This 
  rarely, 
  if 
  ever, 
  occurs 
  about 
  

   the 
  entire 
  circumference 
  of 
  the 
  tree. 
  There 
  are 
  a 
  few 
  cases 
  in 
  which, 
  

   if 
  the 
  expression 
  may 
  be 
  excused, 
  I 
  have 
  traced 
  a 
  missing 
  ring 
  

   entirely 
  around 
  a 
  tree 
  without 
  finding 
  it. 
  I 
  have 
  observed 
  many 
  

   cases 
  in 
  which 
  the 
  missing 
  ring 
  has 
  been 
  evident 
  in 
  less 
  than 
  10 
  

   per 
  cent 
  of 
  the 
  circumference. 
  Some 
  are 
  absent 
  in 
  only 
  a 
  small 
  

   part 
  of 
  their 
  circuit. 
  I 
  have 
  observed 
  change 
  in 
  this 
  respect 
  at 
  

   different 
  heights 
  in 
  the 
  tree, 
  but 
  have 
  not 
  followed 
  that 
  line 
  of 
  

   study 
  further. 
  It 
  is 
  beautifully 
  shown 
  in 
  the 
  longitudinally 
  bisected 
  

   tree. 
  

  

  One 
  sees 
  from 
  this 
  discussion 
  what 
  the 
  probable 
  errors 
  may 
  be 
  

   in 
  mere 
  counting 
  of 
  rings. 
  In 
  the 
  first 
  work 
  on 
  the 
  yellow 
  pines 
  

   the 
  dating 
  was 
  done 
  by 
  simple 
  counting. 
  Accurate 
  dating 
  in 
  the 
  

   same 
  trees 
  (19 
  of 
  them) 
  later 
  on 
  showed 
  that 
  the 
  average 
  error 
  

   in 
  counting 
  through 
  the 
  last 
  200 
  years 
  was 
  4 
  per 
  cent, 
  due 
  prac- 
  

   tically 
  always 
  to 
  missing 
  rings. 
  A 
  comparison 
  in 
  seven 
  sequoias 
  

   between 
  very 
  careful 
  counting 
  and 
  accurate 
  dating 
  in 
  2,000 
  years 
  

   shows 
  an 
  average 
  counting 
  error 
  of 
  35 
  years, 
  which 
  is 
  only 
  1.7 
  

   per 
  cent. 
  

  

  Full 
  confidence 
  in 
  yearly 
  identity 
  really 
  comes 
  from 
  another 
  

   source. 
  The 
  finding 
  of 
  similar 
  distribution 
  of 
  large 
  and 
  small 
  

   rings 
  in 
  practically 
  all 
  individuals 
  of 
  widely 
  scattered 
  groups 
  of 
  

   trees 
  over 
  great 
  periods 
  of 
  time 
  has 
  been 
  evidence 
  enough 
  to 
  make 
  

   us 
  sure. 
  This 
  comparison 
  process 
  between 
  groups 
  of 
  rings 
  in 
  dif- 
  

   ferent 
  trees 
  has 
  received 
  the 
  rather 
  clumsy 
  name 
  of 
  " 
  cross-identifi- 
  

   cation." 
  Cross-identification 
  was 
  first 
  successful 
  in 
  the 
  67 
  Prescott 
  

   trees, 
  then 
  was 
  carried 
  across 
  70 
  miles 
  to 
  the 
  big 
  Flagstaff 
  groups. 
  

   Later 
  it 
  was 
  found 
  to 
  extend 
  225 
  miles 
  further 
  to 
  southwestern 
  

   Colorado 
  with 
  extreme 
  accuracy, 
  90 
  per 
  cent 
  perhaps. 
  This 
  is 
  over 
  

   periods 
  of 
  more 
  than 
  250 
  years. 
  Catalina 
  pines 
  from 
  near 
  Tucson 
  

   have 
  a 
  50 
  per 
  cent 
  likeness 
  to 
  Flagstaff 
  pines. 
  There 
  are 
  many 
  points 
  

   of 
  similarity 
  in 
  the 
  last 
  200 
  years 
  and 
  many 
  differences. 
  Santa 
  

   Rita 
  pines 
  are 
  less 
  like 
  the 
  Flagstaff 
  pines 
  than 
  are 
  the 
  Catalinas. 
  

   In 
  comparison 
  with 
  the 
  California 
  sequoias, 
  differences 
  become 
  

   more 
  common. 
  The 
  superficial 
  resemblance 
  to 
  Arizona 
  pines 
  is 
  5 
  

   or 
  10 
  per 
  cent 
  only. 
  That 
  is, 
  out 
  of 
  every 
  10 
  or 
  20 
  distinctive 
  rings 
  

   with 
  marked 
  individuality, 
  one 
  will 
  be 
  found 
  alike 
  in 
  California 
  

   and 
  Arizona. 
  For 
  example, 
  A. 
  D. 
  1407, 
  1500, 
  1580, 
  1632, 
  1670, 
  

   1729, 
  1782, 
  1822, 
  and 
  1864 
  are 
  small 
  in 
  Arizona 
  pines 
  and 
  Califor- 
  

   nia 
  sequoias. 
  While 
  only 
  a 
  few 
  extreme 
  individual 
  years 
  thus 
  

  

  