﻿32 
  

  

  MR. 
  A. 
  C. 
  SEWARD 
  ON 
  CYCADEOIDEA 
  GIGANTEA. 
  [Feb. 
  1-897, 
  

  

  shoot 
  must 
  unfortunately 
  remain 
  a 
  

  

  veloped 
  fronds 
  or 
  a 
  floral 
  

   matter 
  for 
  speculation. 
  1 
  

  

  It 
  remains 
  for 
  us 
  to 
  consider 
  more 
  fully 
  the 
  affinities 
  of 
  the 
  

   Portland 
  fossil 
  stem. 
  Externally 
  it 
  would 
  be 
  difficult 
  to 
  discover 
  

   any 
  real 
  difference 
  between 
  the 
  fossil 
  and 
  many 
  large 
  trunks 
  of 
  

   recent 
  Cycads, 
  especially 
  some 
  species 
  of 
  Macrozamia 
  and 
  Enceplial- 
  

   artos. 
  In 
  recent 
  stems, 
  the 
  

  

  older 
  petiole-bases 
  may 
  be 
  Pig. 
  4.— 
  The 
  apical 
  bud 
  of 
  Encephal- 
  ■ 
  

   frequently 
  seen 
  to 
  have 
  artos 
  Altensteinii. 
  

  

  rotted 
  away 
  internally, 
  

   while 
  a 
  peripheral 
  band 
  of 
  

   more 
  resistant 
  material, 
  

   periderm 
  or 
  sclerenchyma, 
  

   has 
  remained 
  as 
  a 
  project- 
  

   ing 
  ridge. 
  2 
  In 
  the 
  fossil 
  

   stem 
  it 
  is 
  more 
  particularly 
  

   the 
  interpetiolar 
  tissues 
  

   that 
  have 
  remained 
  as 
  the 
  

   prominent 
  surface-feature. 
  

  

  Passing 
  to 
  the 
  internal 
  

   structure, 
  there 
  is 
  a 
  close 
  

   correspondence 
  between 
  the 
  

   fossil 
  petioles 
  and 
  those 
  of 
  

   living 
  Cycads. 
  In 
  a 
  trans- 
  

   verse 
  section 
  of 
  a 
  recent 
  

   petiole 
  taken 
  some 
  inches 
  

   above 
  the 
  base, 
  there 
  is 
  a 
  

   well-developed 
  hypodermal 
  

   mass 
  of 
  sclerenchyma 
  in- 
  

   terspersed 
  with 
  groups 
  of 
  thin-walled 
  parenchyma. 
  If 
  a 
  series 
  of 
  

   sections 
  be 
  cut 
  from 
  a 
  petiole 
  until 
  the 
  base 
  is 
  reached, 
  the 
  scleren- 
  

   chymatous 
  hypoderm 
  is 
  found 
  to 
  gradually 
  decrease 
  in 
  amount, 
  and 
  

   is 
  finally 
  almost 
  or 
  entirely 
  absent. 
  A 
  cork-cambium 
  arises 
  in 
  the 
  

   persistent 
  basal 
  portion, 
  either 
  in 
  the 
  subepidermal 
  layer 
  orina 
  deeper 
  

   layer 
  of 
  cells, 
  and 
  a 
  ring 
  of 
  periderm 
  is 
  developed. 
  This 
  increase 
  

   in 
  the 
  diameter 
  of 
  the 
  old 
  leaf-bases 
  of 
  Cycads 
  has 
  been 
  alluded 
  to 
  

   by 
  Saporta, 
  3 
  Eenault, 
  4 
  Solms-Laubach, 
  5 
  and 
  others. 
  In 
  the 
  fossil 
  

   stems 
  we 
  have 
  an 
  exactly 
  similar 
  formation 
  of 
  periderm 
  in 
  the 
  

   petiole-bases. 
  The 
  leaf-bases 
  of 
  Dioon 
  eclule, 
  as 
  well 
  as 
  those 
  of 
  

   the 
  species 
  of 
  Macrozamia 
  (M. 
  Denisoni) 
  figured 
  in 
  PL 
  III. 
  fig. 
  2, 
  

   illustrate 
  very 
  clearly 
  the 
  disappearance 
  of 
  the 
  sclerenchyma 
  and 
  the 
  

   formation 
  of 
  cork. 
  In 
  Dioon 
  edule 
  the 
  phellogen 
  occurs 
  internal 
  

  

  1 
  Lester 
  Ward 
  has 
  pointed 
  out 
  (U.S. 
  Geol. 
  Surv., 
  16th 
  Ann. 
  Rep. 
  1896, 
  

   p. 
  487) 
  that 
  one 
  of 
  the 
  specimens 
  of 
  Bennettites 
  (Cycadeoidea) 
  Saxbyana 
  in 
  the 
  

   British 
  Museum 
  possesses 
  an 
  apical 
  leaf 
  -bud. 
  This, 
  however, 
  is 
  very 
  much 
  less 
  

   distinct 
  than 
  the 
  bud 
  in 
  the 
  Portland 
  stem. 
  

  

  2 
  This 
  is 
  particularly 
  well 
  shown 
  in 
  a 
  piece 
  of 
  a 
  stem 
  of 
  Macrozamia 
  

   Moorei 
  in 
  the 
  Museum, 
  Few 
  Gardens. 
  

  

  3 
  Pal. 
  Frang. 
  vol. 
  ii. 
  (1875), 
  Cycadees, 
  p. 
  11. 
  

  

  4 
  ' 
  Cours 
  de 
  Bot. 
  foss.' 
  vol. 
  i. 
  (1885) 
  p. 
  35. 
  

  

  5 
  ' 
  Die 
  Sprossfolge 
  der 
  Stangeria 
  u. 
  der 
  iibrigen 
  Cycadeen,'Bot. 
  Zeit., 
  Jahrg. 
  

   xlviii. 
  p. 
  12. 
  See 
  also 
  Eichler 
  in 
  Engler 
  & 
  Prantl, 
  op. 
  jam 
  cit. 
  p. 
  7. 
  

  

  [From 
  a 
  photograph 
  of 
  a 
  plant 
  in 
  the 
  Palm 
  

   House, 
  Royal 
  G-ardens, 
  Kew.] 
  

  

  