﻿496 
  Derby 
  — 
  Stem 
  Structure 
  of 
  Psaronius 
  Brasiliensis. 
  

  

  The 
  simple 
  form 
  presented 
  by 
  the 
  P 
  strands 
  in 
  the 
  extreme 
  

   cross 
  sections 
  is 
  modified 
  in 
  some 
  of 
  the 
  intermediate 
  ones 
  by 
  

   branching 
  and 
  subdivision. 
  An 
  external 
  branch 
  appears 
  on 
  PI 
  

   at 
  the 
  base 
  of 
  London 
  1, 
  and 
  on 
  P2 
  at 
  the 
  top 
  of 
  London 
  2, 
  

   bnt 
  in 
  neither 
  case 
  does 
  this 
  presist 
  to 
  the 
  succeeding 
  cross 
  sec- 
  

   tion. 
  An 
  internal 
  branch 
  that 
  becomes 
  strongly 
  developed 
  and 
  

   subdivided 
  in 
  the 
  interior 
  parenchyma 
  seems 
  to 
  be 
  a 
  feature 
  

   common 
  to 
  all 
  of 
  this 
  set 
  of 
  strands. 
  This 
  is 
  best 
  seen 
  on 
  the 
  

   PI 
  and 
  P2 
  strands 
  on 
  the 
  faces 
  of 
  the 
  London 
  1 
  and 
  Rio 
  

   slices. 
  In 
  the 
  case 
  of 
  the 
  former 
  the 
  subdivided 
  distal 
  end 
  of 
  

   the 
  branch 
  seems 
  to 
  have 
  soon 
  ceased 
  to 
  grow, 
  while 
  the 
  

   proximal 
  end 
  forms 
  with 
  the 
  reunited 
  shattered 
  portions 
  of 
  the 
  

   parent 
  strand 
  the 
  peculiar 
  open 
  loop 
  seen 
  at 
  the 
  top 
  of 
  the 
  

   Rio 
  slice. 
  In 
  the 
  next 
  cross 
  section 
  above 
  this 
  loop 
  is 
  closed, 
  

   but 
  at 
  the 
  top 
  of 
  the 
  Paris 
  slice 
  it 
  is 
  opened 
  in 
  such 
  a 
  way 
  as 
  

   to 
  restore 
  the 
  simple 
  form 
  of 
  the 
  strand. 
  As 
  each 
  of 
  the 
  other 
  

   strands 
  presents 
  a 
  similar 
  loop 
  in 
  a 
  more 
  or 
  less 
  perfect 
  stage 
  

   of 
  development, 
  this 
  seems 
  to 
  be 
  a 
  normal 
  feature 
  in 
  the 
  growth 
  

   of 
  this 
  set 
  of 
  strands. 
  

  

  The 
  detached 
  subdivisions 
  of 
  the 
  branches 
  of 
  the 
  P 
  strands 
  

   assume 
  the 
  aspect 
  of 
  the 
  smaller 
  members 
  of 
  the 
  central 
  

   group, 
  but 
  as 
  they 
  lie 
  outside 
  of 
  the 
  magic 
  square 
  above 
  noted 
  

   and 
  soon 
  come 
  to 
  an 
  end, 
  a 
  real 
  connection 
  between 
  the 
  P 
  and 
  

   C 
  groups 
  of 
  strands 
  seems 
  improbable. 
  A 
  possible 
  connection 
  

   between 
  the 
  P 
  and 
  F 
  groups 
  is 
  suggested 
  by 
  the 
  relative 
  posi- 
  

   tion 
  of 
  P2 
  and 
  FP 
  on 
  the 
  two 
  faces 
  of 
  the 
  Pio 
  slice 
  and 
  of 
  P3 
  

   and 
  FP 
  on 
  the 
  lower 
  face 
  of 
  the 
  Paris 
  one, 
  but 
  in 
  neither 
  case 
  

   can 
  an 
  actual 
  anastomosis 
  be 
  positively 
  affirmed. 
  

  

  While 
  it 
  seems 
  possible 
  and 
  even 
  probable 
  that 
  anastomoses 
  

   do 
  occur 
  between 
  the 
  P 
  set 
  of 
  strands 
  and 
  one 
  or 
  the 
  other, 
  or 
  

   both, 
  of 
  the 
  two 
  other 
  sets, 
  it 
  is 
  evident 
  that 
  the 
  maintenance 
  

   of 
  such 
  inter-relations 
  cannot 
  be 
  the 
  main 
  function 
  of 
  the 
  

   strongest 
  and 
  most 
  presistent 
  group 
  of 
  vascular 
  strands 
  that 
  

   the 
  plant 
  possessed. 
  Thus 
  the 
  conclusion 
  seems 
  forced 
  upon 
  

   us 
  that 
  the 
  P 
  strands 
  must 
  have 
  supplied 
  external 
  organs 
  that 
  

   constituted 
  a 
  part, 
  and 
  presumably 
  the 
  main 
  part, 
  of 
  the 
  crown 
  

   of 
  the 
  plant. 
  In 
  this 
  case, 
  however, 
  these 
  organs 
  must 
  have 
  

   been 
  presistant 
  during 
  a 
  period 
  of 
  growth 
  longer 
  than 
  that 
  

   represented 
  by 
  the 
  length 
  of 
  the 
  entire 
  fraction 
  of 
  the 
  original 
  

   trunk 
  here. 
  considered; 
  or 
  a 
  substitution 
  of 
  an 
  old 
  set 
  of 
  four 
  

   organs 
  by 
  a 
  new 
  one 
  must 
  have 
  taken 
  place 
  in 
  the 
  zone 
  in 
  which 
  

   the 
  strands 
  are 
  branched 
  and 
  shattered. 
  This 
  last 
  hypothesis 
  

   involves 
  that 
  of 
  a 
  continued 
  upward 
  growth 
  of 
  the 
  sclerenchy- 
  

   mous 
  sheath 
  on 
  the 
  outside 
  of 
  the 
  P 
  strands, 
  whereas 
  in 
  the 
  

   case 
  of 
  the 
  F 
  strands 
  this 
  growth, 
  as 
  shown 
  above, 
  was 
  alter- 
  

   nately 
  on 
  the 
  outer 
  and 
  on 
  the 
  inner 
  side 
  of 
  the 
  strand. 
  

  

  