﻿Derby 
  — 
  Stem 
  Structure 
  of 
  Psaronius 
  Brasiliensis. 
  493 
  

  

  mechanical 
  features 
  do 
  not 
  agree 
  with 
  those 
  of 
  the 
  correspond- 
  

   ing 
  face 
  of 
  the 
  Rio 
  slice. 
  As 
  will 
  be 
  readily 
  seen 
  in 
  fig. 
  2, 
  in 
  

   which 
  the 
  thickness 
  of 
  the 
  various 
  slices 
  and 
  the 
  width 
  

   arbitrarily 
  assigned 
  to 
  the 
  intervals 
  are 
  represented, 
  any 
  inac- 
  

   curacies 
  that 
  there 
  may 
  be 
  in 
  the 
  latter 
  do 
  not 
  materially 
  affect 
  

   the 
  restoration 
  of 
  the 
  original 
  specimen. 
  

  

  Based 
  on 
  careful 
  plotting 
  from 
  photographs 
  of 
  the 
  twelve 
  

   cross 
  sections, 
  Mr. 
  Francisco 
  Basto, 
  draughtsman 
  of 
  the 
  

   Brazilian 
  Geological 
  Service, 
  has 
  prepared 
  the 
  figures 
  given 
  

   on 
  the 
  accompanying 
  plates 
  (Xf). 
  In 
  those 
  of 
  fig. 
  1 
  the 
  central 
  

   stem 
  of 
  the 
  various 
  slices 
  is 
  drawn 
  as 
  if 
  divested 
  of 
  its 
  root 
  

   sheath 
  and 
  inclined 
  at 
  an 
  angle 
  of 
  45 
  degrees, 
  thus 
  giving 
  an 
  

   apparent 
  inequality 
  to 
  the 
  two 
  axes 
  which 
  in 
  reality 
  are 
  sub- 
  

   stantially 
  equal. 
  The 
  real 
  inequality, 
  due 
  to 
  the 
  unequal 
  

   development 
  of 
  the 
  involving 
  root 
  sheath, 
  of 
  the 
  two 
  axes 
  of 
  

   the 
  entire 
  trunk 
  is 
  shown 
  in 
  the 
  ideal 
  longitudinal 
  sections 
  of 
  

   fig. 
  2. 
  In 
  the 
  restoration, 
  fig. 
  3, 
  of 
  the 
  preserved 
  parts 
  of 
  

   one 
  member 
  of 
  each 
  of 
  the 
  three 
  pairs 
  of 
  F 
  strands 
  the 
  figures 
  

   are 
  so 
  placed 
  that 
  if 
  imagined 
  dislocated 
  laterally 
  so 
  as 
  to 
  fall 
  

   into 
  line 
  an 
  almost 
  complete 
  representation 
  of 
  the 
  stem 
  portion 
  

   of 
  a 
  single 
  strand 
  of 
  this 
  group 
  will 
  be 
  obtained. 
  In 
  order 
  to 
  

   permit 
  a 
  better 
  representation 
  of 
  certain 
  features, 
  the 
  interval 
  

   between 
  the 
  Paris 
  and 
  Rio 
  slices 
  has 
  been 
  left 
  open. 
  In 
  

   the 
  designation 
  of 
  the 
  strands 
  Prof. 
  Zeiller's 
  nomenclature 
  of 
  

   P 
  (eripheral) 
  and 
  F 
  (oliar) 
  has 
  been 
  preserved 
  for 
  the 
  two 
  

   outer 
  groups 
  with 
  a 
  modification 
  in 
  the 
  numbering 
  of 
  the 
  latter 
  

   rendered 
  necessary 
  by 
  the 
  introduction 
  of 
  an 
  additional 
  pair 
  

   not 
  known 
  to 
  him, 
  while 
  the 
  central 
  group, 
  of 
  which 
  only 
  the 
  

   outer 
  members 
  are 
  marked, 
  is 
  designated 
  by 
  the 
  letter 
  C. 
  

  

  An 
  inspection 
  of 
  these 
  figures 
  makes 
  it 
  evident 
  that 
  the 
  

   original 
  specimen 
  represented 
  a 
  fragment 
  of 
  a 
  trunk 
  broken 
  

   somewhat 
  above 
  the 
  points 
  of 
  emergence 
  of 
  a 
  pair 
  of 
  oppositely 
  

   placed 
  external 
  organs 
  carrying 
  the 
  vascular 
  strands 
  Fl 
  and 
  F2, 
  

   and 
  again 
  soniewhat 
  above 
  the 
  emergence 
  of 
  a 
  crosswise 
  placed 
  

   pair 
  (F3, 
  F4) 
  of 
  organs 
  of 
  the 
  same 
  kind. 
  Of 
  the 
  last 
  pair 
  the 
  

   strands 
  of 
  F3 
  are 
  completely 
  outside 
  of 
  the 
  sclerenchymous 
  

   sheath 
  on 
  the 
  lower 
  face 
  of 
  the 
  Paris 
  slice, 
  while 
  F4 
  is 
  still 
  

   enclosed 
  within 
  it, 
  and 
  correspondingly 
  the 
  former 
  is 
  seen 
  to 
  

   have 
  disappeared 
  before 
  the 
  level 
  of 
  the 
  upper 
  face 
  of 
  the 
  

   slice 
  was 
  reached, 
  while 
  the 
  latter 
  still 
  persisted 
  at 
  this 
  level, 
  

   showing 
  that 
  an 
  interval 
  of 
  a 
  few 
  millimeters 
  of 
  growth 
  inter- 
  

   vened 
  between 
  the 
  emergence 
  of 
  the 
  two 
  members 
  of 
  each 
  

   pair. 
  On 
  the 
  other 
  hand, 
  the 
  interval 
  between 
  the 
  successive 
  

   pairs 
  of 
  this 
  set 
  was 
  not 
  far 
  from 
  two 
  hundred 
  millimeters. 
  

  

  The 
  numerous 
  strands 
  of 
  the 
  C 
  group 
  are 
  neatly 
  arranged 
  

   in 
  the 
  Strasbourg 
  and 
  London 
  3 
  slices 
  in 
  a 
  loose 
  rectangular 
  

   bundle 
  with 
  a 
  pair 
  of 
  long 
  bounding 
  strands 
  (CI, 
  C2) 
  on 
  the 
  

  

  Am. 
  Jour. 
  Sci.— 
  Fourth 
  Series, 
  Vol. 
  XXXVI, 
  No. 
  215.— 
  November, 
  1913. 
  

   33 
  

  

  