﻿328 
  MR. 
  A. 
  C. 
  SEWARD 
  ON 
  THE 
  ASSOCIATION 
  OF 
  [Aug. 
  1897, 
  

  

  In 
  PL 
  XXIII. 
  fig. 
  2 
  each 
  leaf-scar 
  is 
  more 
  or 
  less 
  completely 
  sur- 
  

   rounded 
  by 
  a 
  narrow 
  sloping 
  plate 
  of 
  sandstone 
  with 
  an 
  irregular 
  

   margin. 
  This 
  is 
  the 
  last 
  of 
  the 
  grooves 
  which 
  separated 
  the 
  leaf- 
  

   scars 
  from 
  one 
  another 
  on 
  the 
  stem-surface. 
  

  

  In 
  text-fig. 
  2e 
  (p. 
  327) 
  a 
  single 
  scar 
  of 
  the 
  stem 
  reproduced 
  in 
  

   PL 
  XXIII. 
  fig. 
  2 
  is 
  draw^n 
  on 
  a 
  larger 
  scale. 
  The 
  scar 
  measures 
  

   6 
  mm. 
  from 
  a 
  to 
  6, 
  and 
  8*5 
  mm. 
  from 
  c 
  to 
  d. 
  At 
  p. 
  p 
  are 
  two 
  slight 
  

   elliptical 
  depressions, 
  and 
  at 
  t 
  a 
  small 
  and 
  laterally 
  elongated 
  scar 
  ; 
  

   the 
  two 
  former 
  represent 
  the 
  familiar 
  oval 
  scars 
  which 
  are 
  character- 
  

   istic 
  of 
  Sigillarian 
  and 
  Lepidodendroid 
  leaf-scars, 
  the 
  latter 
  (t) 
  

   represents 
  the 
  scar 
  of 
  the 
  leaf-trace 
  bundle. 
  The 
  meaning 
  of 
  the 
  

   lower 
  Y-shaped 
  prominence 
  (p) 
  will 
  be 
  more 
  easily 
  explained 
  after 
  

   an 
  examination 
  of 
  other 
  leaf 
  -scars, 
  and 
  a 
  brief 
  reference 
  to 
  the 
  facts 
  

   of 
  internal 
  structure 
  in 
  Lepidodendroid 
  stems. 
  The 
  occurrence 
  of 
  

   the 
  three 
  small 
  marks 
  on 
  the 
  leaf-scars 
  of 
  Sigillaria 
  has 
  long 
  been 
  

   known, 
  but 
  their 
  precise 
  relation 
  with 
  the 
  internal 
  structure 
  has 
  only 
  

   recently 
  been 
  explained. 
  The 
  smaller 
  middle 
  mark 
  has 
  been 
  

   recognized 
  for 
  some 
  time 
  past 
  as 
  that 
  of 
  the 
  leaf-trace 
  bundle, 
  and 
  

   the 
  two 
  larger 
  lateral 
  marks 
  have 
  been 
  described 
  as 
  lateral 
  lacunae 
  l 
  

   consisting 
  of 
  strands 
  of 
  thin- 
  walled 
  and 
  large-celled 
  tissue. 
  Much 
  

   additional 
  light 
  has, 
  however, 
  been 
  thrown 
  on 
  the 
  structure 
  of 
  these 
  

   tissue-strands 
  by 
  the 
  investigations 
  of 
  Williamson, 
  Bertrand, 
  and 
  

   Hovelacque. 
  2 
  Williamson 
  published 
  a 
  detailed 
  account 
  of 
  the 
  struc- 
  

   ture 
  of 
  these 
  tissues 
  in 
  the 
  case 
  of 
  Lepidopliloios 
  and 
  Lepidodendron 
  

   JEFarcourtii. 
  3 
  He 
  found 
  that 
  the 
  vascular 
  tissue 
  of 
  the 
  leaf- 
  trace 
  is 
  

   surrounded 
  by 
  a 
  sheath 
  of 
  delicate 
  parenchyma 
  as 
  it 
  passes 
  through 
  

   the 
  outer 
  cortical 
  tissues 
  of 
  the 
  stem 
  ; 
  in 
  traversing 
  the 
  prosenchyma- 
  

   tous 
  zone 
  of 
  the 
  cortex 
  which 
  is 
  situated 
  immediately 
  internal 
  to 
  the 
  

   leaf-bases, 
  the 
  trace 
  is 
  found 
  to 
  be 
  accompanied 
  by 
  a 
  distinct 
  strand 
  

   of 
  fairly 
  large 
  parenchymatous 
  cells. 
  Soon 
  after 
  leaving 
  the 
  

   prosenchymatous 
  cortical 
  zone, 
  this 
  parenchymatous 
  strand, 
  which 
  

   Bertrand 
  has 
  named 
  the 
  parichnos, 
  4 
  bifurcates, 
  and 
  the 
  two 
  arms 
  

   bend 
  away 
  right 
  and 
  left 
  of 
  the 
  leaf-trace, 
  finally 
  coming 
  to 
  the 
  

   stem-surface 
  as 
  two 
  strands, 
  one 
  on 
  either 
  side 
  of 
  the 
  outgoing 
  

   leaf-bundle. 
  The 
  two 
  lateral 
  marks 
  are 
  therefore 
  the 
  ends 
  of 
  the 
  

   two 
  short 
  arms 
  of 
  the 
  parichnos. 
  It 
  has 
  been 
  suggested 
  that 
  

   the 
  parichnos 
  consists 
  of 
  glandular 
  tissue, 
  and 
  that 
  it 
  may 
  

   serve 
  as 
  ' 
  transpiration-strands.' 
  5 
  Its 
  precise 
  physiological 
  signi- 
  

   ficance 
  is, 
  however, 
  still 
  a 
  matter 
  of 
  doubt. 
  

  

  1 
  See 
  I. 
  Felix, 
  ' 
  Untersuch. 
  iiber 
  d. 
  inneren 
  Ban 
  Westfalisoher 
  Carbon- 
  

   Pflanzen,' 
  Abb., 
  k. 
  Preuss. 
  Geol. 
  Landesanst. 
  vol. 
  vii. 
  (1886) 
  pt. 
  lii. 
  pi. 
  ii. 
  Also 
  

   Renault 
  & 
  Grand' 
  Eury, 
  ' 
  Rech. 
  sur 
  les 
  Veg. 
  silic. 
  d'Autun,' 
  Mein. 
  Acad. 
  Sci. 
  

   vol. 
  xxii. 
  pi. 
  i. 
  

  

  2 
  ' 
  Recbercbes 
  sur 
  ]e 
  Lepidodendron 
  selaginoides, 
  Sternb.,' 
  Mem. 
  Soc. 
  Linn. 
  

   Normandie, 
  vol. 
  xvii. 
  (1892). 
  

  

  3 
  ' 
  On 
  the 
  Organization 
  of 
  the 
  Fossil 
  Plants 
  of 
  the 
  Coal 
  Measures,' 
  pt. 
  xix., 
  Phil. 
  

   Trans, 
  vol. 
  elxxxiv. 
  B 
  (1893). 
  Several 
  figures 
  are 
  given 
  illustrating 
  the 
  structure 
  

   of 
  the 
  leaf-trace 
  and 
  accompanying 
  tissues 
  : 
  some 
  of 
  these 
  are 
  drawn 
  in 
  an 
  

   inverted 
  position. 
  

  

  4 
  ' 
  Remarques 
  sur 
  le 
  Lepidodendron 
  Harcourtiil 
  Trav. 
  et 
  Mem. 
  Facult. 
  

   Lille, 
  vol. 
  ii. 
  (1891) 
  Mem. 
  6, 
  p. 
  84. 
  

  

  5 
  H. 
  Potonie, 
  Ber. 
  Deutsch. 
  bot. 
  Gesellsch. 
  1893, 
  p. 
  325. 
  

  

  