﻿Vol. 
  53.J 
  SIOILLAKIA 
  AND 
  GLOSSOPTER1S 
  IN 
  SOUTH 
  AFEICA. 
  

  

  329 
  

  

  This 
  short 
  account 
  of 
  the 
  parichnos 
  and 
  leaf-trace 
  may 
  render 
  

   easier 
  the 
  interpretation 
  of 
  the 
  appearance 
  presented 
  by 
  the 
  leaf-scars 
  

   of 
  the 
  African 
  stem. 
  In 
  the 
  scar 
  shown 
  in 
  text-fig. 
  2 
  e 
  (p. 
  327), 
  I 
  

   regard 
  the 
  V-shaped 
  projection 
  p' 
  as 
  the 
  cast 
  of 
  the 
  parichnos 
  at 
  

   that 
  point 
  where 
  the 
  two 
  short 
  arms 
  have 
  united 
  into 
  a 
  single 
  strand 
  

   which 
  accompanies 
  the 
  leaf-trace 
  for 
  a 
  short 
  distance 
  through 
  the 
  

   outer 
  cortex. 
  1 
  The 
  two 
  marks 
  p, 
  p 
  represent 
  the 
  ends 
  of 
  the 
  arms. 
  

   The 
  leaf-scars 
  seen 
  in 
  fig. 
  2 
  a 
  show 
  the 
  shape 
  very 
  clearly, 
  also 
  the 
  

   almost 
  complete 
  absence 
  of 
  any 
  leaf- 
  cushions. 
  Atpp 
  there 
  is 
  faintly 
  

   seen 
  the 
  cast 
  of 
  the 
  parichnos-arms, 
  and 
  lower 
  on 
  the 
  leaf-scars 
  

   the 
  prominent 
  cast 
  of 
  the 
  fused 
  arms 
  of 
  the 
  parichnos. 
  In 
  fig. 
  2 
  b 
  

   the 
  crescent-shaped 
  parichnos-cast 
  is 
  very 
  prominent, 
  with 
  a 
  pro- 
  

   jecting 
  knob 
  above 
  it, 
  having 
  a 
  small 
  hole 
  in 
  the 
  centre 
  ; 
  this 
  is 
  also 
  

   seen 
  in 
  fig. 
  2 
  d. 
  The 
  central 
  

  

  hole 
  may 
  represent 
  the 
  posi- 
  Fig. 
  3. 
  — 
  Sigillaria 
  Brardi 
  (Brongn.). 
  

   tion 
  of 
  the 
  harder 
  and 
  more 
  Nat. 
  size. 
  

  

  durable 
  elements 
  of 
  the 
  leaf- 
  

   trace, 
  and 
  the 
  surrounding- 
  

   sandstone 
  may 
  be 
  the 
  cast 
  of 
  

   the 
  cylindrical 
  cavity 
  which 
  

   resulted 
  from 
  the 
  decay 
  of 
  the 
  

   delicate 
  parenchyma 
  accom- 
  

   panying 
  the 
  leaf-bundle. 
  In 
  

   fig. 
  2d 
  the 
  uppermost 
  scar 
  b 
  

   is 
  probably 
  that 
  of 
  the 
  ligule. 
  

   In 
  fig. 
  2 
  c 
  the 
  cast 
  of 
  the 
  

   parichnos 
  is 
  clearly 
  seen 
  as 
  

   a 
  grooved 
  trough 
  -like 
  struc- 
  

   ture 
  containing 
  the 
  cast 
  of 
  

   the 
  leaf-trace 
  t. 
  The 
  thin- 
  

   walled 
  parenchyma 
  of 
  the 
  

   parichnos 
  and 
  the 
  delicate 
  

   cells 
  immediately 
  surrounding 
  

   the 
  leaf-trace 
  would 
  naturally 
  

   decay 
  more 
  readily 
  than 
  the 
  

   harder 
  tissues, 
  and 
  the 
  de- 
  

   pressions 
  or 
  cavities 
  so 
  pro- 
  

   duced 
  being 
  filled 
  in 
  with 
  

   sand 
  have 
  given 
  rise 
  to 
  the 
  

   appearance 
  presented 
  by 
  the 
  

   stem 
  shown 
  in 
  PI. 
  XXIII. 
  

  

  fig. 
  2. 
  If 
  the 
  above 
  interpretation 
  is 
  correct, 
  we 
  have 
  an 
  interesting 
  

   example 
  of 
  the 
  aid 
  afforded 
  by 
  a 
  knowledge 
  of 
  internal 
  structure 
  

   towards 
  the 
  explanation 
  of 
  special 
  features 
  exhibited 
  by 
  structureless 
  

   casts. 
  

  

  The 
  other 
  specimens 
  of 
  this 
  st^m 
  agree 
  in 
  most 
  respects 
  with 
  that 
  

   represented 
  in 
  PL 
  XXIII. 
  fig. 
  2. 
  In 
  some 
  of 
  the 
  casts 
  the 
  surface 
  

  

  1 
  The 
  crescent- 
  sli 
  aped 
  projection 
  shown 
  in 
  a 
  leaf-scar 
  in 
  one 
  of 
  Brongniart's 
  

   figures 
  of 
  Sigillaria 
  Menardi 
  ('Hist. 
  Veg. 
  fuss.' 
  1828, 
  pi. 
  clviii. 
  fig. 
  6 
  a) 
  is 
  possibly 
  

   the 
  cast 
  of 
  the 
  parichnos. 
  

  

  