﻿Derhy 
  — 
  Stem 
  Structure 
  of 
  Psaronius 
  Brasiliensis. 
  497 
  

  

  The 
  cross 
  sections 
  of 
  the 
  stem 
  show 
  a 
  few 
  root 
  sections 
  tra- 
  

   versing 
  the 
  sclerenchymous 
  sheath 
  or 
  situated 
  between 
  it 
  and 
  

   the 
  adjoining 
  P 
  strand, 
  but 
  these 
  are 
  so 
  limited 
  in 
  number 
  as 
  

   compared 
  with 
  the 
  thousands 
  that 
  make 
  up 
  the 
  great 
  root 
  

   sheath 
  encircling 
  the 
  stem, 
  that 
  they 
  must 
  apparently 
  be 
  con- 
  

   sidered 
  as 
  sporadic. 
  This 
  consideration 
  and 
  the 
  fact 
  that 
  the 
  

   roots 
  descend 
  vertically 
  in 
  a 
  space 
  several 
  centimeters 
  wide 
  

   wholly 
  outside 
  of 
  the 
  stem 
  sheath, 
  suggests 
  the 
  hypothesis 
  that 
  

   they 
  arise, 
  for 
  the 
  most 
  part, 
  from 
  the 
  proximal 
  free 
  portion 
  

   of 
  outspreading 
  external 
  organs 
  that 
  formed 
  the 
  crown 
  of 
  the 
  

   plant, 
  and 
  that 
  furthermore 
  these 
  organs 
  must 
  have 
  been 
  sup- 
  

   plied 
  by 
  both 
  the 
  P 
  and 
  the 
  F 
  set 
  of 
  strands. 
  A 
  confirmation 
  

   of 
  this 
  hypothesis 
  appears 
  to 
  be 
  given 
  by 
  the 
  fact 
  that 
  in 
  the 
  

   grooves 
  of 
  the 
  Fio 
  slice 
  the 
  root 
  covering 
  is 
  so 
  loosely 
  adjusted 
  

   to 
  the 
  sclerenchymous 
  sheath 
  that 
  open 
  canals 
  traversing 
  the 
  

   entire 
  slice 
  exist 
  at 
  the 
  bottom 
  of 
  the 
  grooves. 
  The 
  canal 
  on 
  

   the 
  left 
  side 
  is 
  so 
  straight 
  that 
  a 
  large-sized 
  rigid 
  needle 
  can 
  be 
  

   freely 
  passed 
  through 
  it. 
  The 
  other 
  one, 
  though 
  larger, 
  is 
  not 
  

   so 
  freely 
  open, 
  but 
  apparently 
  through 
  a 
  deposit 
  of 
  silica 
  in 
  its 
  

   central 
  portion 
  rather 
  than 
  from 
  root 
  growth 
  within 
  the 
  groove. 
  

  

  Fully 
  cognisant 
  of 
  the 
  deficiencies 
  of 
  my 
  knowledge 
  of 
  

   botany, 
  it 
  is 
  only 
  with 
  the 
  greatest 
  reluctance 
  and 
  in 
  view 
  of 
  

   circumstances 
  that 
  made 
  it 
  almost 
  impossible 
  to 
  confide 
  the 
  

   study 
  of 
  this 
  subject 
  to 
  more 
  competent 
  hands, 
  that 
  I 
  have 
  

   ventured 
  to 
  occupy 
  myself 
  with 
  the 
  present 
  study, 
  in 
  which, 
  

   except 
  in 
  one 
  or 
  two 
  instances, 
  I 
  have 
  refrained 
  from 
  attempts 
  

   at 
  interpretation 
  of 
  the 
  facts 
  observed, 
  as 
  well 
  as 
  from 
  the 
  use 
  

   of 
  a 
  nomenclature 
  that 
  involved 
  such 
  interpretation. 
  In 
  sub- 
  

   mitting 
  the 
  case 
  to 
  the 
  judgment 
  of 
  those 
  competent 
  to 
  judge 
  

   it, 
  I 
  limit 
  myself 
  to 
  recording 
  the 
  fact 
  that 
  in 
  the 
  course 
  of 
  

   this 
  work 
  the 
  apparent 
  analogy 
  of 
  the 
  plant 
  here 
  considered 
  

   with 
  the 
  female 
  representatives 
  of 
  the 
  genus 
  Cycas 
  growing 
  

   about 
  me 
  has 
  been 
  constantly 
  present 
  to 
  my 
  mind. 
  

  

  Eio 
  de 
  Janeiro, 
  Julv 
  12, 
  1913. 
  

  

  