﻿494 
  Derby 
  — 
  Stem 
  Structure 
  of 
  Psaronius 
  Brasiliensis. 
  

  

  longer 
  sides 
  and 
  of 
  short 
  (C3, 
  C4) 
  strands 
  on 
  the 
  shorter 
  one. 
  

   This 
  symmetrical 
  arrangement 
  becomes 
  disorganized 
  higher 
  np 
  

   through 
  the 
  breaking 
  up 
  and 
  subsequent 
  disappearance 
  of 
  the 
  

   longer 
  pair, 
  but 
  is 
  restored, 
  in 
  a 
  reversed 
  position, 
  at 
  the 
  top 
  

   of 
  the 
  Paris 
  slice 
  through 
  the 
  increased 
  development 
  of 
  the 
  

   C3, 
  C4 
  pair 
  and 
  the 
  appearance 
  of 
  a 
  new 
  (Cl',02') 
  pair 
  in 
  sub- 
  

   stitution 
  of 
  the 
  one 
  that 
  was 
  lost. 
  The 
  central 
  group 
  of 
  

   strands 
  thus 
  shows 
  a 
  periodicity 
  at 
  about 
  the 
  same 
  levels 
  as 
  

   that 
  above 
  noted 
  in 
  the 
  F 
  group. 
  

  

  The 
  cut 
  beween 
  the 
  Strasbourg 
  and 
  London 
  3 
  slices 
  caught, 
  

   on 
  its 
  upper 
  side, 
  the 
  beginning 
  of 
  a 
  branch 
  of 
  the 
  CI 
  strand 
  

   and 
  for 
  this 
  reason 
  this 
  strand 
  and 
  its 
  development 
  have 
  been 
  

   selected 
  for 
  restoration. 
  Before 
  reaching 
  the 
  top 
  of 
  the 
  Rio 
  

   slice 
  the 
  parent 
  C 
  strand 
  disappeared 
  while 
  the 
  branch 
  

   developed 
  into 
  a 
  typical 
  F 
  (FP) 
  strand 
  and 
  a 
  pair 
  of 
  scler- 
  

   enchymous 
  bands 
  developed 
  outside 
  of 
  it. 
  At 
  the 
  top 
  of 
  the 
  

   Paris 
  slice 
  this 
  strand 
  and 
  its 
  accompanying 
  sclerenchymous 
  

   bands 
  are 
  so 
  nearly 
  in 
  the 
  same 
  stage 
  of 
  development 
  as 
  the 
  F3 
  

   strand 
  in 
  the 
  Strasbourg 
  slice 
  that 
  the 
  latter 
  may 
  be 
  taken 
  as 
  

   representing 
  its 
  missing 
  portion. 
  On 
  tracing 
  this 
  strand 
  and 
  

   its 
  bands 
  upward 
  their 
  sides 
  are 
  seen 
  to 
  draw 
  inwards 
  until 
  

   they 
  assume 
  the 
  shape 
  presented 
  on 
  the 
  upper 
  face 
  of 
  the 
  Rio 
  

   slice 
  where 
  the 
  portion 
  of 
  the 
  sclerenchymous 
  sheath 
  in 
  front 
  

   of 
  the 
  strand 
  has 
  ceased 
  to 
  form. 
  In 
  the 
  interval 
  between 
  the 
  

   Rio 
  and 
  the 
  Paris 
  slices 
  the 
  internal 
  sclerenchymous 
  bands 
  

   evidently 
  became 
  completely 
  soldered 
  to 
  the 
  outer 
  sheath 
  and 
  

   had 
  their 
  inner 
  margins 
  united 
  so 
  as 
  to 
  make 
  the 
  sheath 
  again 
  

   continuous, 
  while 
  the 
  strand 
  became 
  external 
  and 
  divided 
  into 
  

   two 
  parts 
  through 
  the 
  loss 
  of 
  its 
  central 
  portion. 
  Before 
  

   reaching 
  the 
  top 
  of 
  the 
  Paris 
  slice 
  this 
  strand 
  disappeared, 
  but 
  

   its 
  companion 
  shows 
  one 
  phase 
  of 
  its 
  missing 
  portion 
  and 
  is 
  so 
  

   like 
  the 
  Fl 
  strand 
  in 
  the 
  Strasbourg 
  slice 
  that 
  this 
  may 
  be 
  

   taken 
  as 
  representing 
  the 
  other 
  phases 
  susceptible 
  of 
  preserva- 
  

   tion 
  in 
  the 
  siliciiied 
  trunk 
  of 
  the 
  plant 
  

  

  In 
  view 
  of 
  the 
  history 
  traced 
  above, 
  the 
  Fl, 
  F2 
  pair 
  of 
  

   strands 
  in 
  the 
  four 
  lower 
  slices 
  must 
  be 
  regarded 
  as 
  the 
  

   remnants 
  of 
  presistent 
  stub 
  ends 
  of 
  the 
  stalks 
  of 
  a 
  pair 
  of 
  ex- 
  

   ternal 
  organs 
  that 
  emerged 
  from 
  the 
  trunk 
  somewhat 
  lower 
  

   down 
  and 
  developed 
  parallel 
  with 
  it 
  in 
  deep 
  grooves 
  produced 
  

   by 
  the 
  formation 
  of 
  sclerenchyma 
  behind 
  them, 
  up 
  to 
  near 
  the 
  

   top 
  of 
  the 
  London 
  1 
  slice 
  where 
  the 
  organs 
  spread 
  out 
  laterally 
  

   to 
  form 
  a 
  part 
  of 
  the 
  crown 
  of 
  the 
  plant. 
  Eventually 
  the 
  

   crownpart 
  of 
  these 
  organs 
  fell 
  away, 
  leaving 
  the 
  basal 
  portion 
  

   adherent 
  to 
  the 
  trunk, 
  where 
  they 
  were 
  subsequently 
  covered 
  

   by 
  adventitious 
  roots, 
  descending 
  from 
  above, 
  and 
  thus 
  pro- 
  

   tected 
  from 
  complete 
  decay. 
  Before 
  the 
  formation 
  of 
  the 
  root 
  

   covering 
  these 
  stubs 
  would 
  be 
  exposed 
  to 
  the 
  air 
  and 
  thus 
  

  

  