﻿Brown: 
  Silicious 
  skeleton 
  421 
  

  

  Any 
  tendency 
  of 
  the 
  matrix 
  to 
  shrink 
  or 
  swell 
  along 
  the 
  diameter 
  

   of 
  the 
  fiber, 
  would 
  not 
  be 
  inhibited 
  by 
  the 
  unbranched 
  vertical 
  

   rods, 
  since 
  these 
  would 
  move 
  apart 
  or 
  approach 
  with 
  the 
  swelling 
  

   or 
  shrinking 
  of 
  the 
  matrix. 
  As 
  previously 
  explained, 
  the 
  branching 
  

  

  r 
  

  

  of 
  the 
  skeleton 
  in 
  pit 
  areas 
  would 
  indicate 
  that 
  these 
  areas 
  of 
  the 
  

   wall 
  swell 
  or 
  shrink 
  only 
  in 
  thickness 
  if 
  at 
  all. 
  

  

  IV. 
  EFFECT 
  OF 
  DESILICIFICATION 
  UPON 
  THE 
  MECH- 
  

   ANICAL 
  RIGIDITY 
  OF 
  THE 
  TISSUES 
  

  

  That 
  the 
  silicious 
  skeleton 
  is 
  of 
  fundamental 
  importance 
  to 
  

   the 
  mechanical 
  rigidity 
  of 
  the 
  tissues 
  is 
  indicated 
  by 
  the 
  effect 
  of 
  

   desiliclfication. 
  The 
  haulms 
  of 
  Secale, 
  for 
  example, 
  when 
  placed 
  

   In 
  hydrofluoric 
  acid, 
  contract 
  with 
  elastic 
  force 
  over 
  30 
  per 
  cent 
  

   in 
  length 
  and 
  at 
  the 
  same 
  time 
  expand 
  approximately 
  100 
  per 
  

   cent 
  in 
  diameter. 
  The 
  desiliclfied 
  tissues 
  have 
  a 
  rubber-like 
  

   elasticity 
  and 
  may 
  be 
  stretched 
  nearly 
  to 
  the 
  original 
  length. 
  

  

  Remarkably 
  similar 
  effects 
  are 
  obtained 
  when 
  the 
  xylem 
  of 
  

   Tecoma 
  is 
  desilicified. 
  In 
  the 
  accompanying 
  table 
  (Table 
  I), 
  the 
  

   length 
  of 
  a 
  block 
  of 
  wood 
  and 
  the 
  radial 
  and 
  tangential 
  dimen- 
  

   sion 
  are 
  recorded 
  at 
  indicated 
  intervals 
  during 
  treatment; 
  the 
  

   gain 
  or 
  loss 
  relative 
  to 
  the 
  respective 
  dimensions 
  of 
  the 
  tissue 
  in 
  

   the 
  dry 
  state 
  are 
  incased 
  in 
  parentheses. 
  

  

  The 
  rate 
  and 
  relative 
  amount 
  of 
  swelling 
  or 
  contraction 
  in 
  

   length 
  and 
  in 
  the 
  radial 
  and 
  tangential 
  dimensions 
  of 
  the 
  block, 
  

   the 
  measurements 
  of 
  which 
  are 
  given 
  in 
  the 
  table 
  during 
  the 
  period 
  

   of 
  treatment 
  are 
  shown 
  in 
  the 
  graph, 
  Fig. 
  5. 
  During 
  the 
  five 
  and 
  

   one 
  half 
  hours 
  in 
  boiling 
  water 
  {A 
  to 
  B), 
  the 
  tissues 
  swelled 
  

   barely 
  i 
  per 
  cent 
  in 
  length, 
  though 
  both 
  diameters 
  increased 
  

   more 
  than 
  10 
  per 
  cent. 
  At 
  length, 
  all 
  dimensions 
  became 
  stable 
  

   in 
  water 
  and 
  changed 
  but 
  slightly 
  if 
  at 
  all 
  during 
  the 
  first 
  seventeen 
  

   hours 
  {B 
  to 
  B'), 
  when 
  the 
  water-saturated 
  wood 
  was 
  transferred 
  

  

  to 
  strong 
  hydrofluoric 
  acid. 
  

  

  Up 
  to 
  time 
  B', 
  only 
  the 
  usual 
  phenomena 
  of 
  swelling 
  in 
  woody 
  

   tissues 
  are 
  recorded, 
  of 
  which 
  the 
  relative 
  constancy 
  of 
  length 
  is 
  

   the 
  remarkable 
  but 
  characteristic 
  feature. 
  At 
  B', 
  however, 
  

   changes 
  of 
  an 
  essentially 
  different 
  character 
  began; 
  the 
  length, 
  

   which 
  up 
  to 
  this 
  time 
  had 
  remained 
  almost 
  constant, 
  now 
  rapidly 
  

   contracted 
  over 
  20 
  per 
  cent, 
  while 
  the 
  radial 
  and 
  tangential 
  diam- 
  

   eters 
  expanded 
  over 
  40 
  and 
  over 
  50 
  per 
  cent, 
  respectively. 
  

  

  