﻿Brown: 
  Silicious 
  skeleton 
  

  

  413 
  

  

  dary 
  layer, 
  held 
  in 
  position 
  by 
  what 
  remains 
  of 
  

   the 
  charred 
  matrix 
  (Fig. 
  2, 
  A). 
  In 
  all 
  proba- 
  

   bility 
  the 
  cut 
  ends 
  of 
  these 
  mineralized 
  rods 
  

   are 
  identical 
  with 
  the 
  small 
  non-hygroscopic 
  

   areas 
  which 
  were 
  observed 
  in 
  the 
  untreated 
  

   membrane 
  after 
  being 
  mounted 
  for 
  some 
  time 
  

   in 
  water 
  or 
  glycerine. 
  The 
  material 
  of 
  which 
  

   these 
  tracts 
  in 
  the 
  wall 
  are 
  composed 
  is 
  there- 
  

   fore 
  non-hygroscopic 
  as 
  well 
  as 
  non-combusti- 
  

   ble. 
  The 
  solubility 
  of 
  the 
  rods 
  so 
  isolated 
  was 
  

   tested 
  in 
  various 
  reagents; 
  but 
  such 
  results 
  

   can 
  have 
  little 
  significance 
  as 
  to 
  the 
  original 
  

   composition, 
  since 
  the 
  chemical 
  composition, 
  

   as 
  well 
  as 
  the 
  refractive 
  properties 
  of 
  the 
  rods, 
  

   was 
  found 
  to 
  undergo 
  great 
  change 
  during 
  the 
  

   process 
  of 
  burning. 
  In 
  some 
  cases, 
  the 
  rods 
  

   became 
  covered 
  with 
  a 
  thin 
  film 
  of 
  black 
  ma- 
  

   terial 
  highly 
  resistant 
  to 
  nitric, 
  sulphuric, 
  

   hydrochloric 
  and 
  even 
  hydrofluoric 
  acid. 
  

  

  As 
  will 
  be 
  shown 
  presently, 
  these 
  rods 
  are 
  

   composed, 
  in 
  part 
  at 
  least, 
  of 
  silicious 
  material 
  

   and 
  form 
  a 
  skeleton-like 
  structure 
  in 
  the 
  sec- 
  

   ondary 
  thickening 
  of 
  the 
  fiber 
  wall. 
  The 
  re- 
  

   mainder 
  of 
  the 
  secondar>^ 
  thickening 
  (in 
  which 
  

   the 
  rods 
  are 
  imbedded) 
  may 
  be 
  termed 
  the 
  

   colloidal 
  matrix, 
  for 
  reasons 
  which 
  will 
  be 
  given 
  

   more 
  fully 
  later. 
  

  

  The 
  histology 
  of 
  the 
  secondary 
  thickening 
  

   of 
  the 
  fibers 
  or 
  tracheids 
  in 
  the 
  wood 
  ^nd 
  of 
  

   the 
  fibers 
  of 
  the 
  bast 
  in 
  all 
  

   by 
  the 
  writer 
  is 
  essentially 
  the 
  same 
  as 
  that 
  ob- 
  

   served 
  in 
  the 
  xylem 
  of 
  Tecotna. 
  It 
  is 
  composed 
  

   of 
  the 
  following 
  two 
  structural 
  elements, 
  which 
  

   differ 
  from 
  each 
  other 
  In 
  their 
  physical 
  and 
  

   mechanical 
  properties 
  as 
  well 
  as 
  in 
  their 
  chem- 
  

   ical 
  composition: 
  namely, 
  (i) 
  a 
  non-hygro- 
  

  

  species 
  

  

  scopic 
  silicious 
  skeleton 
  imbedded 
  

  

  in 
  

  

  ( 
  

  

  a 
  

  

  hygroscopic 
  colloidal 
  matrix. 
  With 
  little 
  doubt, 
  

  

  Fig. 
  2, 
  Silicious 
  

   skeleton. 
  diagram- 
  

   matic. 
  A, 
  longitud- 
  

   inal 
  view; 
  B, 
  trans- 
  

   verse 
  view, 
  the 
  shaded 
  

   portion 
  representing 
  

   middle 
  lamella 
  and 
  

   primary 
  thickening. 
  

  

  