﻿26 
  MR. 
  A. 
  C. 
  SEWARD 
  ON 
  CYCADEOIDEA 
  GIGANTEA. 
  [Feb. 
  1 
  897, 
  

  

  occurrence 
  of 
  the 
  secretory 
  tissue 
  is 
  shown 
  by 
  the 
  black 
  dots 
  ; 
  and 
  

   in 
  the 
  parenchyma 
  of 
  the 
  petiole 
  a, 
  shown 
  in 
  fig. 
  14, 
  the 
  sacs 
  are 
  

   seen 
  in 
  longitudinal 
  section 
  as 
  obliquely-running 
  and 
  occasionally 
  

   anastomosing 
  cavities. 
  The 
  parenchymatous 
  tissue 
  of 
  the 
  leaf-stalk 
  

   is 
  usually 
  crushed 
  and 
  imperfect, 
  but 
  in 
  places 
  the 
  preservation 
  is 
  

   sufficiently 
  good 
  to 
  show 
  that 
  the 
  cells 
  were 
  of 
  the 
  ordinary 
  type, 
  

   such 
  as 
  characterizes 
  the 
  fundamental 
  tissue 
  of 
  recent 
  Cycadean 
  

   petioles. 
  In 
  several 
  of 
  the 
  parenchymatous 
  cells 
  of 
  the 
  ground- 
  

   tissue, 
  and 
  especially 
  well 
  seen 
  in 
  longitudinal 
  sections, 
  there 
  occurs 
  

   a 
  light- 
  coloured 
  vacuolated, 
  or 
  in 
  some 
  cases 
  a 
  darker 
  granular 
  

   substance. 
  A 
  few 
  of 
  the 
  cells 
  enclosing 
  such 
  contents 
  are 
  shown 
  

   in 
  PI. 
  IV. 
  figs. 
  11-13; 
  in 
  the 
  cell 
  b 
  (fig. 
  11) 
  the 
  brown 
  contents 
  

   have 
  a 
  granular 
  appearance, 
  and 
  lie 
  in 
  the 
  cell-cavity 
  as 
  a 
  slightly 
  

   ■contracted 
  mass. 
  In 
  the 
  cell 
  c 
  the 
  apparent 
  granular 
  substance 
  

   under 
  a 
  high 
  magnifying 
  power 
  resolves 
  itself 
  into 
  a 
  fine 
  reticulate 
  

   structure, 
  the 
  framework 
  of 
  the 
  net 
  being 
  marked 
  out 
  by 
  lines 
  of 
  

   ■dark 
  granules, 
  and 
  the 
  meshes 
  occupied 
  by 
  a 
  brown 
  substance. 
  In 
  

   fig. 
  13 
  the 
  whole 
  cavity 
  is 
  filled 
  with 
  a 
  lighter 
  and 
  more 
  transparent 
  

   and 
  delicate 
  network, 
  having 
  rather 
  the 
  appearance 
  of 
  a 
  number 
  of 
  

   more 
  or 
  less 
  spherical 
  cells 
  with 
  clear 
  contents. 
  In 
  fig. 
  11 
  d 
  the 
  

   £ell 
  contains 
  a 
  spherical 
  mass 
  bounded 
  by 
  a 
  delicate 
  granular 
  border, 
  

   and 
  consisting 
  of 
  a 
  brown 
  material 
  possessing 
  a 
  vacuolated 
  or 
  

   frothy 
  structure. 
  

  

  Again, 
  in 
  the 
  neighbourhood 
  of 
  the 
  larger 
  sac 
  (fig. 
  12) 
  containing 
  

   the 
  petrified 
  secretion, 
  the 
  cells 
  are 
  occupied 
  by 
  a 
  distinct 
  reticulum. 
  

   The 
  appearance 
  presented 
  by 
  such 
  a 
  cell 
  as 
  d 
  in 
  fig. 
  11 
  and 
  in 
  

   fig. 
  13 
  suggests 
  the 
  spores 
  or 
  cells 
  of 
  an 
  endoparasitic 
  organism, 
  but 
  

   a 
  careful 
  comparison 
  of 
  several 
  cells 
  leads 
  to 
  the 
  conclusion 
  that 
  

   these 
  various 
  forms 
  of 
  vacuolated, 
  frothy, 
  and 
  granular 
  material 
  are 
  

   merely 
  different 
  conditions 
  of 
  cell-contents. 
  Prof. 
  Marshall 
  Ward 
  

   pointed 
  out 
  to 
  me 
  the 
  very 
  striking 
  resemblance, 
  or 
  indeed 
  identity, 
  

   between 
  the 
  contents 
  of 
  the 
  fossil 
  cells 
  and 
  the 
  vacuolated 
  and 
  

   frothy 
  substance 
  found 
  in 
  the 
  parenchymatous 
  tissue 
  of 
  many 
  recent 
  

   plants. 
  In 
  a 
  series 
  of 
  drawings 
  of 
  such 
  cell-contents 
  in 
  some 
  

   recent 
  members 
  of 
  the 
  JRubiacece, 
  made 
  by 
  Prof. 
  Ward 
  from 
  material 
  

   which 
  he 
  investigated 
  in 
  Ceylon, 
  it 
  is 
  possible 
  to 
  recognize 
  the 
  

   several 
  forms 
  assumed 
  by 
  the 
  cell- 
  substance 
  of 
  the 
  fossil 
  parenchyma. 
  

   In 
  the 
  recent 
  tissues 
  these 
  appearances 
  are 
  due 
  to 
  the 
  various 
  forms 
  

   assumed 
  by 
  tannin, 
  oily 
  and 
  protoplasmic 
  substances 
  in 
  the 
  cells, 
  

   and 
  in 
  the 
  fossil 
  cells 
  there 
  can 
  be 
  little 
  doubt 
  that 
  we 
  have 
  an 
  

   illustration 
  of 
  the 
  preservation 
  of 
  similar 
  cell-contents. 
  The 
  chief 
  

   importance 
  of 
  these 
  facts 
  is 
  to 
  emphasize 
  the 
  danger 
  of 
  regarding 
  

   such 
  structures 
  as 
  the 
  cells 
  of 
  foreign 
  organisms. 
  Among 
  recent 
  

   plants 
  this 
  kind 
  of 
  cell-contents 
  has 
  been 
  described 
  as 
  a 
  parasitic 
  

   fungus, 
  and 
  the 
  extraordinary 
  manner 
  in 
  which 
  some 
  portions 
  of 
  the 
  

   vacuolated 
  and 
  frothy 
  substance 
  simulate 
  the 
  rounded 
  cells 
  of 
  a 
  

   fungus, 
  renders 
  it 
  easy 
  to 
  be 
  misled 
  by 
  the 
  deceptive 
  appearance. 
  

   Precisely 
  similar 
  contents 
  occur 
  in 
  the 
  ceris 
  of 
  the 
  ground-tissue 
  in 
  

   the 
  petioles 
  of 
  Bennettites 
  Gibsonianus. 
  

  

  It 
  has 
  recently 
  been 
  shown 
  that 
  the 
  ' 
  spot 
  disease 
  ' 
  of 
  orchids 
  is 
  

  

  