﻿Vol. 
  53.] 
  HE. 
  A. 
  C. 
  SEWARD 
  ON 
  CYCADEOIEEA 
  GIGAXTEA. 
  29 
  

  

  Kraus 
  has 
  figured 
  a 
  stoma 
  of 
  Ceratozamia 
  mexicana 
  x 
  in 
  which 
  the 
  

   guard-cells 
  are 
  curiously 
  curved 
  in 
  such 
  a 
  manner 
  as 
  to 
  present 
  an 
  

   appearance 
  in 
  surface-view 
  similar 
  to 
  that 
  of 
  the 
  fossil 
  stoma. 
  

   Probably, 
  however, 
  the 
  cells 
  s 
  are 
  really 
  separate 
  from 
  the 
  guard- 
  

   cells, 
  and 
  in 
  transverse 
  section 
  would 
  appear 
  very 
  similar 
  to 
  the 
  

   stoma-cells 
  of 
  Cycas 
  revoluta 
  2 
  as 
  figured 
  by 
  Kraus, 
  and 
  later 
  by 
  

   Strasburger. 
  3 
  The 
  latter 
  points 
  out 
  that 
  Kraus's 
  section 
  is 
  neither 
  

   median 
  nor 
  vertical. 
  On 
  the 
  whole 
  the 
  appearance 
  in 
  surface-view 
  

   and 
  the 
  size 
  agree 
  closely 
  with 
  those 
  of 
  the 
  stomata 
  of 
  Dioon 
  edule 
  

   and 
  other 
  Cycads 
  ; 
  in 
  Dioon 
  there 
  are 
  two 
  subsidiary 
  cells 
  accom- 
  

   panying 
  the 
  guard-cells, 
  and 
  it 
  is 
  probable 
  that 
  there 
  are 
  two 
  in 
  the 
  

   stomata 
  of 
  the 
  fossil 
  petioles. 
  So 
  far 
  as 
  it 
  is 
  possible 
  to 
  decide, 
  it 
  

   would 
  appear 
  that 
  in 
  the 
  fossil 
  the 
  stomata 
  are 
  not 
  much 
  below 
  the 
  

   level 
  of 
  the 
  epidermis. 
  

  

  Scattered 
  through 
  the 
  ground-tissue 
  of 
  the 
  portion 
  of 
  the 
  petiole 
  i, 
  

   shown 
  in 
  fig. 
  16, 
  there 
  are 
  twelve 
  imperfectly 
  preserved 
  vascular 
  

   bundles. 
  4 
  The 
  structure 
  of 
  the 
  bundles 
  appears 
  to 
  agree 
  with 
  that 
  

   described 
  by 
  Carruthers 
  5 
  and 
  Lignier 
  6 
  in 
  species 
  of 
  Bennettites. 
  

   A 
  single 
  vascular 
  bundle 
  of 
  Bennettites 
  Gibsonianus 
  is 
  shown 
  in 
  

   PI. 
  IV. 
  fig. 
  10, 
  drawn 
  from 
  one 
  of 
  the 
  sections 
  of 
  this 
  plant 
  in 
  the 
  

   Jodrell 
  Laboratory 
  of 
  the 
  Royal 
  Gardens, 
  Kew. 
  At 
  ejp 
  there 
  is 
  a 
  

   group 
  of 
  tracheids 
  without 
  any 
  regular 
  arrangement, 
  representing 
  the 
  

   centripetal 
  part 
  of 
  the 
  xylem 
  ; 
  the 
  probable 
  position 
  of 
  the 
  protoxylem 
  

   elements 
  is 
  shown 
  zXjpx. 
  External 
  to 
  this 
  there 
  are 
  other 
  tracheids 
  

   more 
  perfectly 
  preserved 
  and 
  arranged 
  in 
  radial 
  series 
  (c/), 
  with 
  a 
  

   few 
  separating 
  rows 
  of 
  medullary-ray 
  cells 
  (m). 
  This 
  portion 
  of 
  

   the 
  bundle 
  constitutes 
  its 
  centrifugally-developed 
  xylem. 
  Beyond 
  

   this 
  the 
  tissues 
  are 
  as 
  a 
  rule 
  less 
  perfectly 
  preserved, 
  but 
  in 
  some 
  of 
  

   the 
  sections 
  of 
  Bennettites 
  it 
  is 
  easy 
  to 
  make 
  out 
  a 
  line 
  of 
  thin- 
  walled 
  

   cambium-cells 
  succeeded 
  by 
  the 
  crushed 
  elements 
  of 
  the 
  phloem. 
  

   Next 
  to 
  the 
  zone 
  of 
  crushed 
  phloem, 
  there 
  is 
  a 
  group 
  of 
  more 
  clearly 
  

   preserved 
  cells 
  (s), 
  which 
  may 
  have 
  been 
  sclerenchymatous 
  ; 
  they 
  

   correspond 
  to 
  the 
  thick-walled 
  elements 
  which 
  Bertrand 
  and 
  Lignier 
  

   have 
  designated 
  the 
  ' 
  fibres 
  primitives 
  ' 
  7 
  ; 
  probably, 
  however, 
  these 
  

   cells 
  do 
  not 
  form 
  part 
  of 
  the 
  true 
  vascular 
  bundle, 
  but 
  belong 
  to 
  

   the 
  ground-tissue 
  of 
  the 
  petiole. 
  In 
  PI. 
  IV. 
  fig. 
  9, 
  one 
  of 
  the 
  

   vascular 
  bundles 
  of 
  the 
  Portland 
  stem 
  is 
  represented 
  ; 
  although 
  the 
  

   preservation 
  of 
  the 
  tissues 
  is 
  imperfect, 
  the 
  structure 
  is 
  sufficiently 
  

   good 
  to 
  enable 
  us 
  to 
  recognize 
  a 
  close 
  agreement 
  with 
  the 
  bundles 
  

   of 
  Bennettites 
  Gibsonianus. 
  The 
  line 
  c 
  marks 
  the 
  external 
  limit 
  of 
  

   the 
  centrifugal 
  xylem 
  and 
  the 
  position 
  of 
  the 
  cambium. 
  External 
  

   to 
  this 
  is 
  the 
  crushed 
  phloem 
  Q?^), 
  and 
  finally 
  a 
  few 
  cells, 
  s, 
  corre- 
  

  

  1 
  Kraus, 
  'Ueber 
  den 
  Bau 
  der 
  Cycadeenfiedern,' 
  Pringsh. 
  Jahrb. 
  vol. 
  iv. 
  

   (1865-66) 
  pi. 
  xxi. 
  fig. 
  20. 
  

  

  2 
  Ibid. 
  pi. 
  xix. 
  fig. 
  5. 
  

  

  3 
  Strasburger, 
  'EinBeitrag 
  zur 
  Entwicklungsgeschichte 
  der 
  Spaltoffnungen,' 
  

   Pringsh. 
  Jahrb. 
  vol. 
  v. 
  (1866-67) 
  p. 
  331, 
  pi. 
  xli. 
  fig. 
  143. 
  

  

  4 
  Not 
  shown 
  in 
  the 
  figure. 
  

  

  5 
  Trans. 
  Linn. 
  Soc. 
  vol. 
  xxvi. 
  (1870) 
  pi. 
  lx. 
  fig. 
  7. 
  

  

  6 
  ' 
  Structure 
  et 
  Affinites 
  du 
  Bennettites 
  Morierei 
  (Sap. 
  & 
  Mar.),' 
  Mem. 
  Soc. 
  

   Linn. 
  Normandie, 
  vol. 
  xviii. 
  (1894) 
  p. 
  21, 
  pi. 
  i. 
  fig. 
  18, 
  etc. 
  

  

  7 
  Lignier, 
  op. 
  supra 
  cit. 
  p. 
  21. 
  

  

  