﻿36 
  ME. 
  A. 
  C. 
  SEWAED 
  ON 
  CTCADEOIDEA 
  GIGANTEA. 
  [Feb. 
  1 
  89 
  7, 
  

  

  bud-scales, 
  and 
  covered 
  with 
  ramental 
  outgrowths. 
  The 
  older 
  part 
  

   of 
  the 
  stem 
  is 
  surrounded 
  by 
  an 
  armour 
  of 
  persistent 
  petiole-bases 
  

   separated 
  one 
  from 
  another 
  by 
  a 
  dense 
  mass 
  of 
  ramenta. 
  The 
  

   petioles 
  composed 
  of 
  parenchymatous 
  ground-tissue 
  with 
  numerous 
  

   secretory 
  cells, 
  and 
  traversed 
  by 
  scattered 
  and 
  comparatively 
  large 
  

   collateral 
  vascular 
  bundles 
  ; 
  the 
  centrif 
  ugally-developed 
  xylem 
  forms 
  

   the 
  most 
  conspicuous 
  part 
  of 
  each 
  bundle, 
  and 
  consists 
  of 
  radially- 
  

   arranged 
  rows 
  of 
  pitted 
  tracheids, 
  with 
  a 
  few 
  rows 
  of 
  medullary- 
  

   ray 
  cells. 
  At 
  the 
  periphery 
  of 
  the 
  petioles 
  there 
  is 
  a 
  fairly 
  thick 
  

   band 
  of 
  phelloderm 
  and 
  periderm, 
  the 
  phellogen 
  being 
  found 
  in 
  

   the 
  subepidermal 
  layer. 
  The 
  epidermis 
  is 
  provided 
  with 
  a 
  distinct 
  

   cuticle, 
  and 
  stomata 
  consisting 
  of 
  two 
  guard-cells 
  and 
  probably 
  two 
  

   subsidiary 
  cells, 
  slightly 
  bent 
  below 
  the 
  level 
  of 
  the 
  epidermis. 
  

   The 
  ramenta 
  arise 
  as 
  epidermal 
  outgrowths 
  in 
  the 
  form 
  of 
  plates 
  

   of 
  elongated 
  parenchymatous 
  cells 
  ; 
  they 
  may 
  consist 
  of 
  a 
  single 
  

   layer 
  of 
  cells, 
  or 
  in 
  the 
  median 
  portion 
  they 
  may 
  be 
  several 
  cells 
  in 
  

   thickness. 
  No 
  trace 
  of 
  any 
  lateral 
  inflorescence 
  such 
  as 
  occurs 
  in 
  

   Bennettites. 
  Fronds 
  unknown. 
  

  

  As 
  already 
  stated, 
  the 
  points 
  of 
  agreement 
  between 
  Cycadeoidea 
  

   gigantea 
  and 
  Bennettites 
  are 
  very 
  clear, 
  with 
  the 
  exception 
  of 
  the 
  

   absence, 
  or 
  apparent 
  absence, 
  in 
  the 
  former 
  of 
  any 
  lateral 
  inflores- 
  

   cence. 
  It 
  is 
  unnecessary 
  to 
  recapitulate 
  the 
  characteristic 
  features 
  

   of 
  Bennettites 
  which 
  mark 
  it 
  off 
  as 
  distinct 
  in 
  certain 
  particulars 
  from 
  

   the 
  recent 
  family 
  Cycadaceae, 
  but 
  it 
  is 
  important 
  to 
  bear 
  in 
  mind 
  

   that 
  in 
  speaking 
  of 
  fossil 
  Cycads 
  we 
  include 
  other 
  forms 
  than 
  those 
  

   which 
  strictly 
  conform 
  to 
  the 
  characters 
  of 
  the 
  present 
  genera. 
  It 
  

   has 
  been 
  rightly 
  said 
  that 
  we 
  have 
  as 
  yet 
  no 
  well-authenticated 
  

   case 
  of 
  a 
  fossil 
  stem 
  which 
  may 
  with 
  certainty 
  be 
  placed 
  in 
  the 
  

   Cycadaceae 
  l 
  as 
  at 
  present 
  defined. 
  As 
  regards 
  the 
  exact 
  affinities 
  

   of 
  Cycadeoidea 
  gigantea, 
  it 
  is 
  impossible 
  to 
  speak 
  with 
  certainty 
  as 
  

   to 
  its 
  natural 
  position 
  without 
  more 
  complete 
  evidence. 
  In 
  the 
  

   absence 
  of 
  the 
  reproductive 
  organs 
  we 
  must 
  be 
  content 
  with 
  such 
  

   evidence 
  as 
  is 
  afforded 
  by 
  the 
  vegetative 
  structures. 
  There 
  is 
  no 
  

   sufficient 
  reason 
  for 
  regarding 
  the 
  stem 
  as 
  essentially 
  distinct 
  from 
  

   such 
  a 
  type 
  as 
  is 
  represented 
  by 
  Bennettites 
  Gibsonianus, 
  so 
  far 
  as 
  

   concerns 
  its 
  position 
  in 
  a 
  system 
  of 
  classification. 
  

  

  It 
  is 
  to 
  be 
  hoped 
  that 
  more 
  material 
  may 
  be 
  obtained 
  which 
  will 
  

   enable 
  us 
  to 
  supply 
  some 
  of 
  the 
  lacunae 
  in 
  the 
  above 
  description, 
  

   and 
  to 
  decide 
  whether 
  Cycadeoidea 
  gigantea 
  agrees 
  in 
  its 
  floral 
  

   structures 
  with 
  existing 
  Cycads 
  or 
  with 
  the 
  true 
  Bennettites, 
  which 
  

   can 
  only 
  be 
  included 
  among 
  Cycadean 
  plants 
  if 
  the 
  term 
  Cycad 
  be 
  

   used 
  in 
  an 
  extremely 
  wide 
  sense. 
  The 
  point 
  of 
  contact 
  between 
  

   Cycadeoidea 
  gigantea 
  and 
  species 
  of 
  Bennettites 
  on 
  the 
  one 
  hand, 
  and 
  

   recent 
  ferns 
  on 
  the 
  other, 
  which 
  is 
  afforded 
  by 
  the 
  ramental 
  scales, 
  

   although 
  perhaps 
  a 
  small 
  one, 
  is 
  of 
  interest 
  when 
  considered 
  in 
  

   connexion 
  with 
  some 
  other 
  fossil 
  genera. 
  The 
  genera 
  Lyginoden- 
  

   dron, 
  Heterangium, 
  Myeloxylon, 
  of 
  Palaeozoic 
  age, 
  are 
  good 
  examples 
  

   of 
  plants 
  in 
  which 
  Cycadean 
  and 
  Filicinean 
  characters 
  are 
  combined 
  

  

  1 
  Solms-Laubach, 
  ' 
  Annals 
  Bot,' 
  vol. 
  v. 
  (1890-91) 
  p. 
  425. 
  

  

  