﻿Derby 
  — 
  Stem 
  Structure 
  of 
  Psaronitis 
  Brasiliensis. 
  495 
  

  

  subject 
  to 
  decay, 
  which 
  seems 
  to 
  have 
  destroyed 
  all 
  their 
  softer 
  

   tissues, 
  leaving 
  only 
  the 
  lignified 
  strands. 
  This 
  conclusion 
  is 
  

   based 
  on 
  the 
  fact 
  that 
  the 
  greater 
  part 
  of 
  the 
  space 
  within 
  the 
  

   grooves 
  is 
  occupied 
  by 
  open 
  cavities 
  or 
  by 
  a 
  filling 
  of 
  silica 
  in 
  

   which 
  traces 
  of 
  organic 
  structure 
  are 
  obscure 
  or 
  lacking. 
  

   Aside 
  from 
  the 
  F 
  strands, 
  which 
  are 
  tolerably 
  distinct 
  in 
  these 
  

   grooves, 
  a 
  number 
  of 
  rounded 
  spots 
  occur 
  that 
  look 
  like 
  cross 
  

   sections 
  of 
  roots, 
  but 
  which 
  may 
  prove 
  to 
  be 
  accidental. 
  As 
  

   the 
  doubt 
  regarding 
  the 
  true 
  character 
  of 
  these 
  markings 
  can 
  

   only 
  be 
  resolved 
  by 
  a 
  microscopic 
  examination, 
  which 
  there 
  is 
  

   no 
  opportunity 
  of 
  making, 
  they 
  have 
  been 
  left 
  out 
  of 
  account 
  

   in 
  the 
  restoration. 
  

  

  The 
  mode 
  of 
  formation 
  of 
  the 
  sclerenchymous 
  sheath 
  behind 
  

   the 
  emergent 
  organ 
  is 
  shown 
  in 
  the 
  seven 
  lower 
  sections 
  of 
  the 
  

   trunk. 
  In 
  the 
  interval 
  between 
  the 
  incurved 
  sides 
  of 
  the 
  in- 
  

   ternal 
  sclerenchymous 
  bands 
  aligned 
  shreds 
  of 
  sclerenchyma 
  

   appear 
  which 
  continue 
  detached 
  until 
  the 
  fall 
  of 
  the 
  organ, 
  

   when 
  they 
  unite 
  with 
  each 
  other 
  and 
  with 
  the 
  bands 
  and 
  thus 
  

   become, 
  with 
  these, 
  an 
  integral 
  part 
  of 
  the 
  trunk 
  sheath. 
  

  

  It 
  is 
  to 
  be 
  noted 
  that 
  the 
  cross 
  sections 
  present 
  no 
  indications 
  

   of 
  a 
  sclerenchymous 
  covering 
  of 
  the 
  stem 
  of 
  the 
  organ 
  itself, 
  

   from 
  which 
  it 
  may 
  be 
  concluded 
  that 
  this, 
  aside 
  from 
  being 
  

   ephemeral, 
  could 
  have 
  had 
  no 
  great 
  extension, 
  giving 
  it 
  a 
  con- 
  

   siderable 
  weight, 
  in 
  its 
  missing 
  outspreading 
  portion, 
  since 
  its 
  

   only 
  mechanical 
  support 
  seems 
  to 
  have 
  been 
  that 
  afforded 
  by 
  

   the 
  vascular 
  strands. 
  

  

  The 
  four 
  P 
  strands 
  are 
  essentially 
  alike 
  in 
  the 
  uppermost 
  

   cross 
  section 
  of 
  the 
  trunk,* 
  w 
  T 
  here 
  each 
  presents 
  the 
  form 
  of 
  a 
  

   broad 
  ribbon 
  slightly 
  arched 
  in 
  its 
  central 
  portion 
  and 
  strongly 
  

   inrolled 
  at 
  the 
  margins, 
  with 
  a 
  loose 
  semicircular 
  curve 
  on 
  one 
  

   side 
  and 
  a 
  more 
  compressed 
  semielliptical 
  one 
  on 
  the 
  other. 
  

   With 
  a 
  reversal 
  in 
  the 
  position 
  of 
  the 
  two 
  types 
  of 
  inrolling, 
  

   this 
  simple 
  form 
  of 
  the 
  ribbon 
  recurs 
  also 
  in 
  the 
  lower 
  cross 
  

   sections, 
  in 
  which, 
  however, 
  there 
  is 
  a 
  departure 
  from 
  symme- 
  

   try 
  through 
  the 
  division 
  of 
  P3 
  into 
  two 
  parts 
  which 
  become 
  

   united 
  in 
  the 
  interior 
  of 
  the 
  London 
  2 
  slice, 
  though 
  the 
  pecu- 
  

   liar 
  loop 
  of 
  the 
  smaller 
  division 
  presists 
  for 
  some 
  time 
  and 
  the 
  

   strand 
  only 
  becomes 
  normal 
  at 
  the 
  top 
  of 
  London 
  1. 
  It 
  is 
  to 
  

   be 
  noted 
  that 
  the 
  compressed 
  subelliptical 
  inrolled 
  margin 
  of 
  

   these 
  strands 
  lies 
  between 
  the 
  trunk 
  sheath 
  and 
  an 
  internal 
  

   sclerenchymous 
  band 
  where 
  this 
  stands 
  subparallel 
  to 
  the 
  

   sheath. 
  

  

  * 
  As 
  noted 
  above 
  this 
  cross 
  section 
  has 
  only 
  been 
  partially 
  cut 
  so 
  that 
  it 
  

   presents, 
  in 
  part, 
  an 
  irregular 
  fractured 
  surface 
  on 
  which 
  some 
  of 
  its 
  struc- 
  

   tural 
  features 
  do 
  not 
  appear 
  clearly 
  in 
  the 
  photograph 
  at 
  hand. 
  I 
  owe 
  to 
  

   the 
  extreme 
  kindness 
  of 
  Prof. 
  Zeiller 
  an 
  accurate 
  sketch 
  of 
  the 
  stem 
  portion 
  

   of 
  this 
  cross 
  section. 
  

  

  