﻿472 
  J. 
  Bari^ell 
  — 
  Upper 
  Devonian 
  Delta. 
  

  

  seasonal 
  dryness 
  though 
  not 
  aridity, 
  and 
  the 
  absence 
  of 
  annual 
  

   rings, 
  may 
  seem 
  somewhat 
  contradictory. 
  If 
  the 
  adjustment 
  

   be 
  sought 
  by 
  modifying 
  the 
  conclusions 
  in 
  regard 
  to 
  climate, 
  

   a 
  condition 
  of 
  perennial 
  intermittent 
  rainfall 
  may 
  be 
  substituted 
  

   for 
  seasonal 
  rains. 
  Such 
  a 
  shorter 
  rhythm, 
  measured 
  by 
  days 
  

   or 
  weeks 
  rather 
  than 
  by 
  seasons, 
  may 
  be 
  so 
  adjusted 
  as 
  to 
  give 
  

   opportunity 
  for 
  drying 
  and 
  oxidation, 
  but 
  without 
  stoppage 
  of 
  

   vegetable 
  growth. 
  A 
  delicately 
  balanced 
  condition 
  such 
  as 
  

   this 
  would, 
  however, 
  be 
  expected 
  to 
  pass 
  in 
  some 
  regions, 
  as 
  

   previously 
  noted, 
  into 
  markedly 
  humid 
  conditions, 
  or 
  in 
  others 
  

   into 
  marked 
  aridity, 
  and 
  give 
  rise 
  to 
  a 
  climatic 
  variety 
  of 
  

   which 
  there 
  is 
  not 
  evidence 
  in 
  the 
  Devonian. 
  

  

  If 
  the 
  adjustment 
  be 
  sought 
  within 
  the 
  limits 
  of 
  vegetal 
  

   adaptation, 
  two 
  suggestions 
  may 
  be 
  offered. 
  First, 
  is 
  it 
  possible 
  

   that 
  perennial 
  plants 
  of 
  that 
  time 
  may 
  have 
  possessed 
  such 
  a 
  

   nature 
  as 
  not 
  to 
  have 
  recorded 
  by 
  rings 
  the 
  stoppage 
  of 
  growth 
  ? 
  

   This 
  is 
  a 
  question 
  for 
  paleobotanists 
  to 
  answer. 
  The 
  most 
  

   probable 
  explanation, 
  however, 
  to 
  the 
  writer 
  seems 
  to 
  lie 
  in 
  the 
  

   proposition 
  that 
  at 
  that 
  time 
  perennial 
  and 
  arboreal 
  vegetation 
  

   was 
  restricted 
  to 
  regions 
  of 
  perpetually 
  available 
  ground-water. 
  

   In 
  a 
  climate 
  without 
  freezing 
  winters 
  it 
  was 
  thus 
  not 
  affected 
  

   by 
  the 
  coming 
  and 
  going 
  of 
  rains. 
  This 
  view 
  receives 
  some 
  

   support, 
  so 
  far 
  as 
  the 
  writer 
  has 
  observed, 
  from 
  the 
  distribution 
  

   of 
  the 
  plant 
  fossils. 
  The 
  impressions 
  of 
  tree 
  trunks 
  and 
  of 
  

   strap-like 
  leaves 
  on 
  the 
  whole 
  are 
  rare, 
  but 
  where 
  they 
  do 
  occur 
  

   are 
  found 
  in 
  decolorized 
  shales 
  or 
  sandstones. 
  Not 
  infrequently 
  

   coaly 
  streaks 
  mark 
  their 
  presence. 
  These 
  may 
  be 
  regarded 
  as 
  

   the 
  deposits 
  of 
  swamps 
  or 
  marginal 
  to 
  river 
  channels. 
  The 
  red 
  

   shales, 
  on 
  the 
  other 
  hand, 
  are 
  doubtless 
  the 
  deposits 
  of 
  flood 
  

   plains, 
  dried 
  out 
  during 
  a 
  part 
  of 
  the 
  year, 
  air 
  taking 
  the 
  place 
  of 
  

   water 
  in 
  the 
  soil. 
  In 
  these 
  deposits 
  indistinct 
  tendril-like 
  mark- 
  

   ings 
  are 
  not 
  uncommon, 
  traceable 
  only 
  by 
  faint 
  changes 
  in 
  luster 
  

   and 
  texture, 
  not 
  by 
  the 
  presence 
  of 
  deoxidation. 
  They 
  are 
  sel- 
  

   dom 
  as 
  definite 
  as 
  in 
  the 
  example 
  shown 
  in 
  fig. 
  4, 
  but 
  suggest 
  

   either 
  the 
  thread-like 
  burrows 
  of 
  small 
  worms, 
  or 
  the 
  small 
  

   rootlets 
  of 
  an 
  herbaceous 
  vegetation. 
  Such 
  an 
  areal 
  distribu- 
  

   tion 
  of 
  arboreal 
  and 
  herbaceous 
  vegetation 
  in 
  alluvial 
  regions 
  

   is 
  that 
  in 
  fact 
  which 
  tends 
  to 
  take 
  place 
  to-day 
  within 
  those 
  

   parts 
  of 
  the 
  tropics 
  marked 
  by 
  pronounced 
  dry 
  seasons, 
  but 
  the 
  

   present 
  differentiation 
  and 
  adaptation 
  of 
  trees 
  to 
  a 
  wide 
  range 
  

   of 
  environments 
  apparently 
  makes 
  the 
  environmental 
  control 
  

   less 
  compulsory 
  than 
  in 
  Paleozoic 
  times. 
  Then 
  the 
  local 
  com- 
  

   bination 
  of 
  perpetual 
  ground-water 
  and 
  perpetual 
  warmth 
  may 
  

   have 
  stimulated 
  in 
  the 
  rivalry 
  for 
  sunlight 
  the 
  striving 
  upward 
  

   of 
  sporophytes, 
  creating 
  the 
  first 
  of 
  trees 
  and 
  the 
  truly 
  pri- 
  

   meval 
  forest. 
  

  

  Yale 
  University. 
  

  

  