﻿Yol. 
  53.] 
  ME. 
  A. 
  C. 
  SEWARD 
  ON" 
  CTCADEOIDEA 
  GIGANTEA. 
  25 
  

  

  with 
  remarkable 
  distinctness 
  ; 
  he 
  named 
  this 
  stem 
  Bennettites 
  

   dacoiensis, 
  but 
  Lester 
  Ward 
  has 
  substituted 
  the 
  generic 
  term 
  

   Cycadeoidea. 
  1 
  The 
  distal 
  ends 
  of 
  the 
  persistent 
  petiole-bases 
  have 
  

   the 
  form 
  of 
  rhomboidal 
  areas, 
  and 
  the 
  more 
  internal 
  portions 
  ex- 
  

   tend 
  for 
  a 
  short 
  distance 
  towards 
  the 
  centre 
  of 
  the 
  stem 
  in 
  a 
  

   slightly 
  upward 
  direction. 
  This 
  is, 
  at 
  all 
  events, 
  the 
  case 
  in 
  the 
  

   middle 
  and 
  lower 
  portion 
  of 
  the 
  specimen, 
  but 
  this 
  position 
  of 
  the 
  

   petioles 
  is 
  probably 
  to 
  a 
  large 
  extent 
  the 
  result 
  of 
  the 
  pressure 
  of 
  

   overlying 
  fronds, 
  which 
  has 
  imparted 
  to 
  the 
  bases 
  a 
  slightly 
  down- 
  

   ward 
  direction. 
  

  

  A 
  closer 
  examination 
  of 
  the 
  surface-features 
  and 
  of 
  the 
  facts 
  

   revealed 
  by 
  microscopic 
  sections 
  of 
  such 
  peripheral 
  tissues 
  as 
  have 
  

   been 
  preserved 
  brings 
  out 
  some 
  interesting 
  points, 
  which 
  enable 
  us 
  

   to 
  institute 
  a 
  comparison 
  with 
  recent 
  plants 
  and 
  other 
  fossil 
  Cycads. 
  

   In 
  PL 
  II. 
  fig. 
  2 
  a 
  portion 
  of 
  the 
  surface 
  towards 
  the 
  lower 
  part 
  of 
  

   the 
  trunk 
  is 
  shown 
  on 
  a 
  larger 
  scale. 
  The 
  appearance 
  is 
  that 
  of 
  a 
  

   strong 
  and 
  prominent 
  network 
  with 
  rhomboidal 
  or 
  elliptical 
  meshes; 
  

   the 
  upper 
  and 
  lower 
  sides 
  of 
  each 
  mesh 
  assume 
  in 
  some 
  places 
  the 
  

   form 
  of 
  an 
  arc 
  of 
  a 
  circle, 
  and 
  laterally 
  each 
  mesh 
  is 
  bounded 
  by 
  

   the 
  upper 
  and 
  lower 
  walls 
  meeting 
  at 
  an 
  acute 
  angle. 
  The 
  meshes 
  

   shown 
  in 
  the 
  figure 
  (on 
  a 
  reduced 
  scale) 
  have 
  a 
  breadth 
  of 
  about 
  3 
  cm. 
  

   and 
  a 
  height 
  of 
  2 
  cm. 
  In 
  many 
  cases 
  the 
  spaces 
  in 
  the 
  network 
  are 
  

   occupied 
  by 
  a 
  plug 
  of 
  cherty 
  rock 
  which 
  can 
  occasionally 
  be 
  extracted 
  

   without 
  difficulty 
  ; 
  in 
  others 
  there 
  is 
  a 
  mass 
  of 
  crumbling 
  brown 
  dust, 
  

   while 
  some 
  are 
  empty 
  and 
  extend 
  for 
  a 
  short 
  distance 
  into 
  the 
  stem, 
  

   as 
  cavities 
  marking 
  the 
  position 
  of 
  the 
  lowest 
  portion 
  of 
  the 
  petioles. 
  

   In 
  some 
  of 
  the 
  plugs 
  occupying 
  the 
  meshes 
  several 
  small 
  pits 
  or 
  

   dots 
  may 
  be 
  seen 
  towards 
  the 
  periphery 
  ; 
  these 
  are, 
  no 
  doubt, 
  the 
  

   remains 
  of 
  the 
  vascular 
  bundles 
  of 
  the 
  leaf-stalk. 
  In 
  most 
  cases, 
  

   however, 
  the 
  actual 
  structure 
  of 
  the 
  petioles 
  has 
  not 
  been 
  preserved 
  

   in 
  any 
  detail. 
  The 
  projecting 
  framework 
  frequently 
  shows 
  a 
  

   marked 
  tendency 
  to 
  weather 
  into 
  flakes, 
  and 
  this 
  is 
  simply 
  an 
  ex- 
  

   pression 
  of 
  the 
  fact 
  that 
  the 
  ridges 
  separating 
  the 
  petiole-bases 
  are 
  

   largely 
  made 
  up 
  of 
  laminar 
  structures, 
  which 
  are 
  arranged 
  in 
  a 
  

   direction 
  parallel 
  to 
  the 
  surface 
  of 
  the 
  petioles. 
  These 
  interpetiolar 
  

   structures 
  are 
  diagrammatically 
  shown 
  in 
  PL 
  Y. 
  figs. 
  14 
  r, 
  16-18 
  r, 
  

   and 
  more 
  highly 
  magnified 
  in 
  PL 
  III. 
  fig. 
  1 
  r, 
  and 
  figs. 
  4 
  & 
  8. 
  

   Sections 
  cut 
  through 
  some 
  of 
  the 
  projecting 
  ridges, 
  of 
  which 
  the 
  

   structure 
  has 
  been 
  preserved 
  by 
  the 
  infiltration 
  of 
  siliceous 
  solutions, 
  

   enable 
  us 
  to 
  make 
  out 
  some 
  of 
  the 
  anatomical 
  characters 
  of 
  the 
  

   petioles 
  and 
  the 
  surrounding 
  tissue 
  composing 
  the 
  greater 
  part 
  of 
  

   the 
  framework 
  of 
  the 
  net. 
  The 
  petioles 
  consist 
  in 
  the 
  main 
  of 
  

   fairly 
  large-celled 
  parenchymatous 
  tissue, 
  traversed 
  by 
  numerous 
  

   secretory 
  canals 
  and 
  scattered 
  vascular 
  bundles. 
  The 
  position 
  of 
  

   the 
  secretory 
  sacs 
  or 
  canals 
  is 
  indicated 
  by 
  the 
  occurrence 
  of 
  dark 
  

   brown 
  or 
  almost 
  black 
  patches 
  which 
  represent 
  the 
  mineralized 
  

   contents 
  of 
  the 
  secretory 
  tissue. 
  In 
  PL 
  Y. 
  figs. 
  16-18 
  the 
  manner 
  of 
  

  

  1 
  Proc. 
  Biol. 
  Soe. 
  Washington, 
  vol. 
  ix. 
  (1894) 
  p. 
  86. 
  

  

  