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  Brown: 
  Silicious 
  skeleton 
  

  

  which 
  IS 
  an 
  accurate 
  drawing 
  of 
  A 
  after 
  desilicification. 
  Usu- 
  

   ally 
  the 
  contracting 
  fibers 
  increase 
  much 
  more 
  in 
  diameter 
  to- 
  

   ward 
  the 
  center 
  than 
  near 
  the 
  ends, 
  as 
  has 
  been 
  accurately 
  shown 
  

   in 
  C 
  and 
  D, 
  In 
  any 
  case 
  the 
  secondary 
  thickening 
  of 
  the 
  fibers 
  

   contracts 
  in 
  length 
  and 
  expands 
  in 
  diameter 
  with 
  an 
  elastic 
  force 
  

   sufficient 
  to 
  separate 
  this 
  thickening 
  from 
  the 
  primary 
  thicken- 
  

   ing, 
  and 
  to 
  burst 
  the 
  mdidle 
  lamella, 
  medullary 
  rays 
  and 
  other 
  

   parts 
  of 
  the 
  woody 
  tissue 
  sufficiently 
  to 
  allow 
  the 
  transverse 
  ex- 
  

   pansion. 
  

  

  After 
  the 
  dissolution 
  of 
  the 
  silicious 
  skeleton 
  the 
  colloid 
  

   matrix 
  is 
  gelatin-like 
  in 
  texture, 
  without 
  mechanical 
  rigidity, 
  and 
  

   assumes 
  various 
  curved 
  outlines 
  as 
  shown 
  in 
  B, 
  C, 
  and 
  D. 
  It 
  

   absorbs 
  water 
  freely, 
  and, 
  when 
  dried, 
  shrinks 
  greatly 
  in 
  both 
  

   diameter 
  and 
  length 
  as 
  shown 
  in 
  E, 
  Fig. 
  4, 
  which 
  is 
  an 
  accurate 
  

   drawing 
  of 
  D 
  after 
  drying. 
  The 
  contraction 
  in 
  diameter 
  is 
  more 
  

   accurately 
  shown 
  in 
  FiG. 
  i, 
  B, 
  which 
  represents 
  the 
  remains 
  of 
  A 
  

   after 
  desilicification 
  and 
  drying. 
  The 
  primary 
  thickening 
  and 
  

   middle 
  lamella 
  (n) 
  are 
  broken 
  into 
  fragments 
  but 
  shrink 
  compara- 
  

   tively 
  little 
  (n'). 
  

  

  The 
  structure 
  of 
  the 
  colloidal 
  matrix 
  may 
  be 
  observed 
  in 
  de- 
  

   silicified 
  fibers 
  mounted 
  in 
  water. 
  Owing 
  to 
  differences 
  in 
  refrac- 
  

   tion, 
  delicate 
  spiral 
  lines 
  of 
  material 
  may 
  be 
  observed 
  in 
  the 
  

   body 
  of 
  the 
  matrix 
  as 
  shown 
  in 
  Fig. 
  4, 
  C 
  Further 
  evidence 
  of 
  

   the 
  spiral 
  structure 
  of 
  the 
  colloidal 
  matrix 
  is 
  found 
  in 
  the 
  inclina- 
  

   tion 
  of 
  the 
  slit-like 
  orifices 
  of 
  the 
  fiber 
  pits, 
  which 
  coincides 
  with 
  

   that 
  of 
  the 
  spirals. 
  

  

  III. 
  INHIBITING 
  EFFECT 
  OF 
  SKELETON 
  UPON 
  THE 
  

  

  SWELLING 
  OF 
  THE 
  MATRIX 
  

  

  Since 
  the 
  non-hygroscopic 
  skeleton 
  rods 
  would 
  remain 
  constant 
  

   in 
  length 
  with 
  the 
  varying 
  moisture 
  content 
  of 
  the 
  matrix, 
  they 
  

   would 
  inhibit 
  any 
  tendency 
  of 
  the 
  matrix 
  to 
  swell 
  or 
  shrink 
  longi- 
  

   tudinally, 
  except 
  in 
  so 
  far 
  as 
  would 
  be 
  permitted 
  by 
  their 
  elasticity. 
  

   With 
  the 
  application 
  of 
  force, 
  a 
  certain 
  amount 
  of 
  longitudinal 
  

   compression 
  or 
  stretching 
  of 
  the 
  skeleton 
  rods 
  would 
  undoubtedly 
  

   be 
  permitted; 
  hence 
  the 
  slight 
  longitudinal 
  swelling 
  and 
  shrinking 
  

   of 
  woody 
  tissues, 
  which 
  at 
  most 
  amounts 
  to 
  only 
  i 
  to 
  2 
  per 
  

   cent, 
  may 
  take 
  place 
  by 
  reason 
  of 
  the 
  elastic 
  property 
  of 
  the 
  rods. 
  

  

  