﻿NATURAL 
  RUBBER 
  — 
  COOK 
  389 
  

  

  lateral 
  branch. 
  The 
  leaves 
  of 
  the 
  branches 
  are 
  like 
  those 
  that 
  subtend 
  

   the 
  lateral 
  branches 
  on 
  the 
  original 
  trunk. 
  

  

  From 
  a 
  morphological 
  viewpoint 
  the 
  lateral 
  branches 
  of 
  Castilla 
  

   may 
  be 
  interpreted 
  as 
  inflorescences 
  that 
  have 
  developed 
  a 
  special 
  

   form 
  of 
  leaves 
  and 
  assumed 
  a 
  major 
  proportion 
  of 
  the 
  vegetative 
  

   functions. 
  This 
  appears 
  strikingly 
  in 
  the 
  young 
  trees, 
  the 
  lower 
  

   lateral 
  branches 
  growing 
  to 
  the 
  greatest 
  length, 
  often 
  10 
  or 
  12 
  feet, 
  

   and 
  yet 
  not 
  bearing 
  any 
  flowers 
  or 
  fruits. 
  The 
  shorter 
  laterals, 
  far- 
  

   ther 
  up 
  the 
  trunk, 
  most 
  of 
  them 
  only 
  3 
  to 
  4 
  feet 
  long, 
  produce 
  flowers 
  

   or 
  fruits 
  in 
  a 
  continuous 
  series, 
  except 
  on 
  a 
  few 
  of 
  the 
  basal 
  joints. 
  

  

  The 
  long 
  laterals 
  of 
  the 
  lower 
  part 
  of 
  the 
  trunk 
  may 
  be 
  compared 
  

   to 
  the 
  spreading 
  rosette 
  leaves 
  of 
  many 
  herbaceous 
  plants. 
  A 
  wide 
  

   expanse 
  of 
  foliage 
  is 
  formed 
  on 
  young 
  trees 
  standing 
  in 
  open 
  places 
  

   where 
  the 
  branches 
  have 
  full 
  sunlight 
  and 
  develop 
  symmetrically 
  

   so 
  that 
  the 
  ground 
  underneath 
  is 
  well 
  shaded. 
  An 
  adaptive 
  function 
  

   of 
  the 
  specialized 
  branching 
  is 
  seen 
  in 
  the 
  rapid 
  and 
  continuous 
  de- 
  

   velopment 
  of 
  further 
  new 
  sections 
  of 
  the 
  trunk, 
  each 
  with 
  its 
  lateral 
  

   branch, 
  and 
  these 
  in 
  turn 
  soon 
  replacing 
  those 
  lower 
  down. 
  The 
  

   young 
  trees 
  are 
  of 
  striking 
  appearance, 
  regular 
  in 
  form 
  and 
  vivid 
  in 
  

   color. 
  Apart 
  from 
  the 
  interest 
  in 
  rubber, 
  Castilla 
  trees 
  might 
  well 
  

   be 
  planted 
  around 
  schools 
  in 
  southern 
  Florida, 
  and 
  in 
  other 
  tropical 
  

   countries, 
  to 
  facilitate 
  the 
  study 
  of 
  the 
  vegetative 
  specializations. 
  

  

  SPECIALIZED 
  LEAVES 
  OF 
  DIMORPHIC 
  BRANCHES 
  

  

  As 
  previously 
  indicated, 
  the 
  leaves 
  of 
  lateral 
  branches 
  of 
  Castilla 
  

   are 
  different 
  from 
  those 
  of 
  the 
  main 
  trunk 
  and 
  the 
  permanent 
  

   branches. 
  The 
  oblong 
  form, 
  the 
  pinnate 
  venation, 
  and 
  the 
  short 
  

   petioles 
  are 
  the 
  outstanding 
  features 
  of 
  the 
  lateral-branch 
  leaves. 
  

   Compared 
  with 
  the 
  leaves 
  of 
  the 
  lateral 
  branches, 
  those 
  of 
  the 
  trunk 
  

   and 
  the 
  permanent 
  branches 
  are 
  relatively 
  short 
  and 
  broad, 
  and 
  the 
  

   petioles 
  notably 
  longer. 
  The 
  venation 
  of 
  the 
  trunk 
  leaves 
  is 
  mark- 
  

   edly 
  different, 
  being 
  palmate 
  rather 
  than 
  pinnate, 
  with 
  a 
  basal 
  vein 
  

   on 
  each 
  side 
  more 
  oblique 
  and 
  longer 
  than 
  the 
  others. 
  The 
  secondary 
  

   veins 
  along 
  the 
  lower 
  side 
  of 
  these 
  long 
  primaries 
  are 
  much 
  stronger 
  

   than 
  other 
  secondary 
  veins, 
  sometimes 
  attaining 
  a 
  length 
  of 
  more 
  

   than 
  2 
  inches. 
  The 
  leaves 
  of 
  the 
  trunk 
  and 
  its 
  permanent 
  branches 
  

   often 
  appear 
  as 
  reduced 
  or 
  rudimentary. 
  Some 
  of 
  them 
  are 
  only 
  

   4 
  or 
  5 
  inches 
  long 
  and 
  less 
  than 
  3 
  inches 
  broad. 
  Such 
  leaves 
  may 
  be 
  

   seen 
  only 
  on 
  new 
  growth, 
  since 
  they 
  usually 
  turn 
  yellow 
  and 
  fall 
  off 
  

   in 
  a 
  few 
  weeks. 
  On 
  other 
  trees 
  the 
  trunk 
  leaves 
  may 
  be 
  nearly 
  as 
  

   wide 
  as 
  the 
  branch 
  leaves 
  but 
  only 
  half 
  the 
  length, 
  broadly 
  shouldered 
  

   or 
  angled 
  at 
  the 
  side, 
  with 
  less 
  than 
  half 
  the 
  number 
  of 
  primary 
  veins, 
  

   and 
  the 
  large 
  basal 
  vein 
  on 
  each 
  side 
  strongly 
  developed. 
  

  

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