﻿Brown: 
  Silicious 
  skeleton 
  423 
  

  

  r 
  

  

  The 
  transverse 
  dimensions 
  subsequently 
  contracted 
  to 
  some 
  ex- 
  

  

  tent, 
  but 
  after 
  a 
  few 
  hours 
  all 
  dimensions 
  remained 
  nearly 
  constant, 
  

  

  whether 
  left 
  in 
  acid, 
  or 
  transferred 
  to 
  water 
  (C 
  to 
  D). 
  The 
  

  

  subsequent 
  great 
  contraction 
  (Z>) 
  of 
  all 
  dimensions 
  which 
  took 
  

  

  place 
  when 
  the 
  desilicified 
  tissues 
  were 
  dried, 
  indicates 
  the 
  almost 
  

  

  complete 
  loss 
  of 
  mechanical 
  rigidity 
  of 
  the 
  xylem 
  after 
  desilicifi- 
  

   cation. 
  

  

  The 
  changes 
  which 
  occur 
  in 
  the 
  longitudinal 
  dimensions 
  of 
  a 
  

   block 
  of 
  the 
  xylem 
  of 
  Tecoma 
  during 
  treatment 
  are 
  essentially 
  

   the 
  same 
  as 
  those 
  which 
  occur 
  in 
  the 
  isolated 
  fiber 
  under 
  the 
  same 
  

   treatment. 
  Probably 
  up 
  to 
  time 
  B' 
  the 
  skeleton 
  rods 
  had 
  not 
  

   been 
  weakened 
  by 
  the 
  acid. 
  But 
  immediately 
  after 
  B^ 
  there 
  was 
  a 
  

   rapid 
  contraction 
  in 
  length 
  and 
  expansion 
  in 
  the 
  transverse 
  dimen- 
  

   sions, 
  such 
  as 
  would 
  occur 
  with 
  the 
  collapse 
  of 
  the 
  skeletons; 
  the 
  

   entire 
  course 
  of 
  the 
  curves 
  during 
  the 
  first 
  part 
  of 
  the 
  time, 
  B^ 
  C, 
  in- 
  

   dicate 
  the 
  collapse 
  of 
  the 
  mechanical 
  element 
  of 
  the 
  xylem. 
  

  

  A 
  similar 
  amount 
  of 
  longitudinal 
  contraction 
  and 
  transverse 
  

   expansion 
  occurred 
  in 
  the 
  xylem 
  of 
  all 
  of 
  the 
  thirty 
  lapachol- 
  

   yielding 
  samples 
  of 
  Tecoma 
  examined. 
  Similar 
  changes 
  were 
  

   observed 
  in 
  approximately 
  one-fifth 
  of 
  the 
  species 
  of 
  the 
  other 
  

   genera 
  and 
  families 
  examined 
  by 
  the 
  writer; 
  but 
  the 
  amount 
  

   varied 
  with 
  the 
  genus 
  and 
  species. 
  Many 
  species 
  such 
  as 
  Aspidos- 
  

   permas, 
  showed 
  little 
  or 
  no 
  longitudinal 
  contraction 
  during 
  desilicifi- 
  

   cation. 
  Such 
  differences 
  in 
  the 
  effect 
  of 
  desilicification 
  are 
  

   reasonably 
  explained 
  on 
  the 
  assumption 
  that 
  the 
  rods 
  must 
  differ 
  

   in 
  chemical 
  composition, 
  according 
  to 
  the 
  species, 
  although 
  

   silicious 
  material 
  may 
  be 
  present 
  in 
  each 
  case. 
  

  

  V. 
  SUMMARY 
  . 
  

  

  The 
  longitudinal 
  dimensions 
  of 
  the 
  xylem 
  and 
  bast 
  in 
  either 
  

   living 
  or 
  dead 
  tissues 
  are 
  subject 
  to 
  little 
  variation 
  upon 
  soaking 
  

  

  dry 
  

  

  ary 
  

  

  This 
  skeleton 
  is 
  com- 
  

  

  posed 
  of 
  sparingly 
  branched 
  non-hygroscopic 
  rods 
  of 
  silicified 
  

   material 
  which 
  extend 
  longitudinally 
  in 
  the 
  hygroscopic 
  cell-mem- 
  

   brane 
  from 
  one 
  end 
  of 
  the 
  fiber 
  or 
  tracheid 
  to 
  the 
  other 
  

  

  Except 
  for 
  local 
  areas, 
  the 
  longitudinal 
  skeleton 
  rod? 
  are 
  not 
  

   branched 
  or 
  united 
  in 
  a 
  way 
  to 
  prevent 
  them 
  from 
  being 
  spread 
  

  

  