﻿Vol. 
  53.] 
  ME. 
  A. 
  C. 
  SEWAED 
  OK 
  CZCADEOIDEA 
  GIGASTTEA. 
  27 
  

  

  of 
  a 
  non-parasitic 
  nature 
  x 
  ; 
  the 
  contents 
  of 
  the 
  leaf-cells 
  of 
  diseased 
  

   plants 
  agree 
  very 
  closely 
  with 
  those 
  in 
  the 
  fossil 
  tissue. 
  In 
  a 
  

   paper 
  contributed 
  by 
  Prof. 
  "Williamson 
  in 
  1888 
  to 
  the 
  ' 
  Annals 
  of 
  

   Botany 
  ' 
  several 
  examples 
  are 
  described 
  of 
  ' 
  anomalous 
  cells 
  ' 
  

   within 
  the 
  tissues 
  of 
  Coal-Measure 
  plants. 
  2 
  Some 
  of 
  the 
  figures 
  

   of 
  these 
  structures 
  are 
  practically 
  identical 
  with 
  the 
  appearance 
  

   presented 
  by 
  the 
  vacuolated 
  contents 
  in 
  the 
  cells 
  of 
  the 
  Cycadean 
  

   petioles. 
  A 
  comparison, 
  for 
  example, 
  of 
  Williamson's 
  fig. 
  1 
  

   {pi. 
  xviii.) 
  with 
  figures 
  11-13, 
  PI. 
  IV. 
  of 
  this 
  paper, 
  and 
  again 
  

   with 
  Massee's 
  figure 
  of 
  the 
  leaf-cells 
  of 
  a 
  recent 
  orchid, 
  brings 
  

   out 
  an 
  exceedingly 
  close 
  agreement 
  in 
  both 
  these 
  cases. 
  There 
  is 
  

   very 
  little 
  doubt 
  that 
  many 
  of 
  these 
  so-called 
  ' 
  cells 
  ' 
  in 
  the 
  tissues 
  of 
  

   fossil 
  plants 
  are 
  in 
  reality 
  vacuoles, 
  granules, 
  and 
  other 
  structures 
  

   which 
  are 
  probably 
  pathological 
  in 
  their 
  origin. 
  Some 
  may 
  be 
  

   normal 
  cell-contents, 
  but 
  others 
  are 
  more 
  probably 
  the 
  expression 
  

   of 
  some 
  abnormal 
  condition 
  of 
  the 
  plant 
  in 
  which 
  they 
  occur. 
  

  

  In 
  some 
  of 
  the 
  parenchymatous 
  cells 
  in 
  the 
  petioles 
  of 
  the 
  Port- 
  

   land 
  fossil 
  there 
  are 
  preserved 
  small 
  oval 
  or 
  spherical 
  bodies 
  which 
  

   stand 
  out 
  fairly 
  conspicuously 
  in 
  the 
  cell-cavity, 
  as 
  at 
  n, 
  PI. 
  IV. 
  

   fig. 
  11. 
  It 
  is 
  not 
  improbable 
  that 
  these 
  are 
  examples 
  of 
  fossil 
  nuclei. 
  

  

  At 
  the 
  periphery 
  of 
  the 
  petioles 
  the 
  ground-tissue 
  passes 
  

   gradually 
  into 
  a 
  parenchyma 
  composed 
  of 
  somewhat 
  smaller 
  cells 
  

   (PI. 
  III. 
  fig. 
  1), 
  which 
  assume 
  a 
  distinct 
  radial 
  arrangement. 
  

   External 
  to 
  these 
  innermost 
  radially 
  disposed 
  cells 
  the 
  tissue 
  is 
  

   frequently 
  broken 
  across, 
  but 
  in 
  places 
  it 
  has 
  been 
  left 
  intact, 
  and 
  

   is 
  then 
  seen 
  to 
  have 
  the 
  form 
  of 
  a 
  zone 
  of 
  smaller, 
  thinner-walled, 
  

   and 
  flattened 
  cells, 
  which 
  is 
  evidently 
  a 
  band 
  of 
  meristematic 
  tissue. 
  

   Beyond 
  the 
  cambium 
  layer 
  there 
  is 
  a 
  succession 
  of 
  flatter 
  and 
  often 
  

   crushed 
  cells 
  in 
  regular 
  series, 
  limited 
  by 
  a 
  layer 
  of 
  indistinct 
  and 
  

   partially 
  disorganized 
  cells 
  (e) 
  representing 
  the 
  remnants 
  of 
  an 
  

   epidermis. 
  In 
  some 
  parts 
  of 
  the 
  section 
  a 
  light 
  yellow-coloured 
  

   line 
  (c) 
  may 
  be 
  seen 
  outside 
  the 
  epidermal 
  cells, 
  and 
  this 
  is 
  in 
  all 
  

   probability 
  the 
  imperfectly 
  preserved 
  and 
  broken 
  cuticle 
  which 
  has 
  

   in 
  many 
  places 
  been 
  detached 
  from 
  the 
  cells 
  of 
  the 
  epidermis. 
  The 
  

   dark 
  bands 
  (p) 
  at 
  the 
  margins 
  of 
  the 
  petioles 
  in 
  PL 
  V. 
  figs. 
  16-18, 
  

   and 
  the 
  band 
  (p) 
  in 
  fig. 
  14, 
  are 
  made 
  up 
  of 
  radial 
  rows 
  of 
  tan- 
  

   gentially-flattened 
  cells. 
  

  

  In 
  PL 
  III. 
  fig. 
  1 
  the 
  lowest 
  and 
  largest 
  cells 
  g 
  are 
  part 
  of 
  the 
  

   parenchymatous 
  ground-tissue 
  of 
  the 
  petiole 
  ; 
  next 
  to 
  these 
  occur 
  

   Tather 
  smaller 
  and 
  radially-arranged 
  cells, 
  with 
  cell-contents 
  of 
  a 
  

   bright 
  sherry 
  -colour, 
  which 
  may 
  be 
  described 
  as 
  phelloderm 
  (plid.) 
  

   formed 
  on 
  the 
  inner 
  side 
  of 
  the 
  cork-cambium 
  or 
  phellogen 
  (phi.). 
  

   The 
  break 
  in 
  the 
  tissues 
  represents 
  approximately 
  the 
  position 
  of 
  

   the 
  cambium-cells, 
  which 
  would 
  form 
  a 
  natural 
  line 
  of 
  weakness. 
  

   External 
  to 
  this, 
  we 
  have 
  the 
  lighter-coloured 
  and 
  flatter 
  cells 
  ck., 
  

   which 
  constitute 
  the 
  cork-tissue 
  developed 
  from 
  the 
  phellogen. 
  

   The 
  rich 
  brown 
  contents 
  of 
  the 
  phelloderm-cells 
  no 
  doubt 
  consist 
  

   of 
  the 
  silicified 
  protoplasmic 
  contents 
  of 
  this 
  recently 
  developed 
  

  

  1 
  a. 
  Massee, 
  « 
  Annals 
  Bot.' 
  vol. 
  ix. 
  (1895) 
  p. 
  421, 
  pi. 
  xv. 
  

  

  2 
  W. 
  C. 
  Williamson, 
  ' 
  Annals 
  Bot.' 
  vol. 
  i. 
  (1888) 
  p.' 
  1, 
  pi. 
  xviii. 
  

  

  