﻿408 
  Brown: 
  Silicious 
  skeleton 
  

  

  vary 
  independently 
  of 
  another. 
  Nothing 
  in 
  the 
  relative 
  size, 
  

   shape, 
  or 
  arrangement 
  of 
  the 
  cells 
  would 
  bring 
  about 
  a 
  result 
  of 
  

   this 
  kind, 
  ' 
  

  

  _ 
  r 
  

  

  In 
  a 
  strand 
  of 
  bast, 
  for 
  example, 
  it 
  is 
  difficult 
  to 
  conceive 
  of 
  

   any 
  change 
  in 
  the 
  dimensions 
  of 
  the 
  tissue 
  as 
  a 
  whole 
  which 
  would 
  

   not 
  involve 
  a 
  corresponding 
  change 
  in 
  the 
  dimensions 
  of 
  each 
  

   component 
  fiber, 
  and 
  this 
  statement 
  would 
  apply 
  equally 
  to 
  the 
  

   xylem. 
  Hence 
  it 
  is 
  apparent 
  that 
  the 
  basis 
  for 
  an 
  explanation 
  of 
  

   the 
  phenomena 
  of 
  swelling 
  and 
  shrinking 
  in 
  these 
  mechanical 
  

   tissues 
  must, 
  in 
  its 
  last 
  analysis, 
  He, 
  not 
  in 
  the 
  structure 
  of 
  the 
  

   tissue 
  as 
  composed 
  of 
  cells, 
  hut 
  in 
  ^he 
  structure 
  of 
  the 
  membrane 
  

   as 
  a 
  part 
  of 
  the 
  cell. 
  

  

  During 
  the 
  years 
  1917-1920, 
  the 
  writer 
  devoted 
  a 
  portion 
  of 
  

   the 
  time 
  to 
  a 
  study 
  of 
  the 
  minute 
  structure 
  of 
  the 
  thickened 
  mem- 
  

  

  f 
  ' 
  ■ 
  _ 
  

  

  branes 
  which 
  characterize 
  the 
  mechanical 
  tissues 
  of 
  the 
  stem, 
  

   and 
  in 
  the 
  course 
  of 
  this 
  work 
  the 
  probable 
  explanation 
  of 
  the 
  

   phenomena 
  just 
  described 
  became 
  apparent. 
  It 
  was 
  found 
  that 
  

   longitudinal 
  tracts 
  In 
  the 
  secondary 
  thickening 
  of 
  the 
  wall 
  in 
  the 
  

   fibers 
  and 
  tracheids 
  of 
  the 
  wood 
  and 
  In 
  the 
  fibers 
  of 
  the 
  bast 
  are 
  

   more 
  highly 
  minerahzed 
  than 
  the 
  material 
  of 
  which 
  the 
  rest 
  of 
  the 
  

   wall 
  is 
  composed. 
  These 
  mineralized 
  tracts 
  or 
  rods, 
  in 
  which 
  

   silicious 
  material 
  appears 
  always 
  to 
  be 
  present, 
  run 
  longitudinally 
  

   from 
  one 
  end 
  of 
  the 
  fiber 
  to 
  the 
  other 
  and 
  constitute 
  a 
  skeleton- 
  

   like 
  structure 
  (see 
  Fig. 
  3) 
  which, 
  there 
  is 
  every 
  reason 
  to 
  believe, 
  

   must 
  have 
  a 
  direct 
  effect 
  upon 
  the 
  physical 
  and 
  mechanical 
  

   properties 
  of 
  the 
  fiber 
  or 
  tracheld 
  in 
  the 
  walls 
  of 
  which 
  It 
  is 
  im- 
  

   bedded. 
  ^ 
  In 
  contrast 
  to' 
  the 
  other 
  parts 
  of 
  the 
  wall 
  substance, 
  

   these 
  silicious 
  rods 
  imbibe 
  little 
  or 
  no 
  water 
  and 
  hence 
  would 
  

   neither 
  swell 
  nor 
  shrink 
  with 
  such 
  variation 
  in 
  the 
  amount 
  of 
  imbi- 
  

   bition 
  water 
  as 
  may 
  take 
  place 
  In 
  the 
  hygroscopic 
  colloidal 
  material 
  

   in 
  which 
  they 
  are 
  imbedded, 
  as 
  In 
  a 
  matrix'. 
  The 
  matrix, 
  on 
  the 
  

   other 
  hand, 
  absorbs 
  water 
  freely, 
  so 
  that 
  the 
  dry 
  llgnified 
  walls 
  

   according 
  to 
  Pfeffer,* 
  may 
  take 
  up 
  as 
  much 
  as 
  51 
  per 
  cent 
  of 
  their 
  

   weight 
  m 
  water. 
  Presumably 
  the 
  colloidal 
  material 
  tends 
  to 
  

   swell 
  equally 
  in 
  its 
  different 
  axes 
  during 
  imbibition; 
  but 
  the 
  mech- 
  

   anics 
  of 
  movement 
  permltte 
  _d_by^gi^sillc^^ 
  in 
  relation 
  

  

  • 
  PfeiTer. 
  W. 
  The 
  physiology 
  of 
  plants; 
  English 
  translation. 
  Oxford. 
  Vol. 
  

  

  I 
  , 
  p. 
  209- 
  

  

  