﻿Brown: 
  Silicious 
  skeleton 
  409 
  

  

  to 
  the 
  colloidal 
  matrix 
  is, 
  to 
  all 
  appearance, 
  such 
  as 
  would 
  almost 
  

   inhibit 
  any 
  tendency 
  of 
  the 
  fiber 
  or 
  tracheid 
  to 
  swell 
  or 
  shrink 
  

  

  + 
  

  

  longitudinally. 
  Since, 
  however, 
  the 
  rods 
  of 
  the 
  skeleton 
  are 
  not 
  

   generally 
  connected 
  laterally 
  and 
  would 
  therefore 
  be 
  free 
  to 
  move 
  

   apart 
  or 
  approach 
  more 
  closely 
  to 
  one 
  another, 
  they 
  would 
  allow 
  

   the 
  matrix 
  in 
  the 
  spaces 
  between 
  to 
  swell 
  or 
  shrink 
  along 
  any 
  of 
  

   the 
  transverse 
  diameters 
  of 
  the 
  fibers. 
  

  

  These 
  details 
  in 
  the 
  structure 
  of 
  the 
  cell-wall 
  make 
  it 
  clear 
  

   that 
  the 
  shrinking 
  or 
  swelling 
  of 
  the 
  Xylem 
  or 
  bast 
  would 
  not 
  ma- 
  

   terially 
  change 
  the 
  longitudinal 
  dimensions 
  of 
  these 
  tissues. 
  

   Hence 
  the 
  ' 
  fiber-walls 
  of 
  living 
  tissues, 
  as 
  soon 
  as 
  the 
  silicious 
  

   skeletons 
  are 
  formed, 
  may 
  function 
  in 
  the 
  difTusion 
  and 
  transport 
  

   of 
  liquid 
  solutions 
  or 
  may 
  swell 
  or 
  slirink 
  in 
  diameter 
  with 
  the 
  

   increase 
  or 
  decrease 
  of 
  imbibition 
  water, 
  with 
  the 
  fluctuations 
  of 
  

   turgor 
  in 
  the 
  cells, 
  or 
  with 
  the 
  changes 
  of 
  sap 
  pressure 
  in 
  the 
  con- 
  

   ducting 
  elements; 
  at 
  the 
  same 
  time 
  they 
  may 
  offer 
  the 
  undimin- 
  

   ished 
  resistance 
  to 
  longitudinal 
  tension 
  or 
  compression 
  ' 
  necessary 
  

   for 
  the 
  mechanical 
  support 
  of 
  the 
  stem. 
  Except 
  for 
  decay, 
  the 
  

   changes 
  which 
  take 
  place 
  with 
  the 
  death 
  of 
  the 
  cell 
  — 
  in 
  the 
  

   haulms 
  of 
  rye 
  and 
  other 
  grasses 
  after 
  the 
  ripening 
  of 
  the 
  seed 
  or 
  

   in 
  the 
  xylem 
  of 
  the 
  tree 
  after 
  one 
  or 
  more 
  years^do 
  not 
  materially 
  

   afifect 
  the 
  structural 
  or 
  physical 
  properties 
  of 
  these 
  tissues. 
  

  

  The 
  writer 
  is 
  indebted 
  to 
  Professors 
  A. 
  W. 
  Evans, 
  G. 
  E. 
  

   Nichols, 
  and 
  other 
  members 
  of 
  the 
  Department 
  of 
  Botany 
  for 
  

   material 
  and 
  for 
  many 
  valued 
  suggestions 
  and 
  criticisms 
  through- 
  

   out 
  the 
  investigation;' 
  to 
  Professor 
  H. 
  N. 
  Whi,tford 
  and 
  other 
  

  

  me 
  

  

  other 
  woody 
  plants; 
  and 
  to 
  Professors 
  A. 
  J. 
  Hill 
  of 
  the 
  Depart- 
  

   ment 
  of 
  Chemistry 
  and 
  W. 
  E. 
  Ford 
  of 
  the 
  Department 
  of 
  Mineral- 
  

   ogy, 
  to 
  whom 
  portions 
  of 
  the 
  work 
  have 
  been 
  submitted 
  for 
  criti- 
  

  

  cism. 
  

  

  II. 
  HISTOLOGICAL 
  ELEMENTS 
  OF 
  TRACHEIDS 
  AND 
  

  

  FIBERS 
  

  

  In 
  the 
  course 
  of 
  

  

  ondary 
  

  

  in 
  some 
  cases, 
  the 
  bast 
  of 
  approximately 
  five 
  hundred 
  species 
  

  

  examined 
  

  

  the 
  fiber 
  wall 
  in 
  all 
  was 
  found 
  to 
  be 
  essentially 
  the 
  same. 
  Of 
  

  

  