﻿NATURAL 
  RUBBER 
  — 
  COOK 
  387 
  

  

  tissues 
  of 
  the 
  bark, 
  but 
  it 
  appears 
  that 
  sap 
  as 
  well 
  as 
  latex 
  exudes 
  

   in 
  the 
  tapping 
  cuts 
  and 
  that 
  the 
  two 
  are 
  mixed, 
  to 
  the 
  detriment 
  of 
  

   the 
  rubber. 
  

  

  SPECIALIZED 
  BRANCHES 
  AND 
  LEAVES 
  IN 
  CASTILLA 
  

  

  Botanical 
  textbooks 
  do 
  not 
  prepare 
  us 
  to 
  appreciate 
  the 
  vegeta- 
  

   tive 
  specializations 
  of 
  plants. 
  The 
  floral 
  organs 
  in 
  many 
  families 
  

   are 
  highly 
  specialized 
  and 
  have 
  been 
  studied 
  in 
  great 
  detail, 
  while 
  

   little 
  account 
  has 
  been 
  taken 
  of 
  different 
  forms 
  of 
  branches 
  and 
  leaves, 
  

   even 
  among 
  agricultural 
  plants 
  where 
  pecularities 
  of 
  the 
  vegetative 
  

   organs 
  often 
  determine 
  methods 
  of 
  culture 
  or 
  pruning. 
  Several 
  ex- 
  

   amples 
  of 
  two 
  distinct 
  kinds 
  of 
  branches 
  were 
  described 
  in 
  a 
  publica- 
  

   tion 
  of 
  the 
  United 
  States 
  Department 
  of 
  Agriculture 
  in 
  1911, 
  Bulletin 
  

   198, 
  "Dimorphic 
  Branches 
  of 
  Tropical 
  Crop 
  Plants; 
  Cotton, 
  Coffee, 
  

   Cacao, 
  the 
  Central 
  American 
  Rubber 
  Tree, 
  and 
  the 
  Banana." 
  

   Specialized 
  branching 
  habits 
  in 
  the 
  Para 
  rubber 
  tree 
  were 
  also 
  re- 
  

   ported 
  in 
  1930. 
  

  

  The 
  vegetative 
  parts 
  of 
  plants, 
  like 
  the 
  flowers 
  themselves, 
  are 
  

   formed 
  as 
  a 
  succession 
  of 
  equivalent 
  structural 
  units, 
  known 
  to 
  mor- 
  

   phologists 
  as 
  metamers 
  or 
  phytomers. 
  Each 
  unit 
  consists 
  theoret- 
  

   ically 
  of 
  two 
  structural 
  elements, 
  a 
  stem 
  section 
  or 
  caulomer, 
  and 
  a 
  

   leaf 
  section 
  or 
  phyllomer. 
  Either 
  of 
  these 
  elements 
  may 
  be 
  sup- 
  

   pressed, 
  but 
  both 
  are 
  present 
  in 
  normal 
  vegetative 
  metamers. 
  It 
  is 
  

   usual 
  to 
  think 
  of 
  the 
  vegetative 
  metamers 
  as 
  all 
  alike, 
  and 
  of 
  floral 
  

   metamers 
  as 
  of 
  many 
  forms. 
  In 
  reality 
  the 
  vegetative 
  metamers 
  are 
  

   capable 
  of 
  being 
  as 
  definitely 
  specialized 
  as 
  the 
  floral 
  metamers, 
  some 
  

   as 
  preceding 
  the 
  flowers, 
  others 
  as 
  forming 
  specialized 
  branches. 
  

  

  Not 
  only 
  the 
  structures 
  and 
  functions 
  of 
  two 
  kinds 
  of 
  branches 
  are 
  

   different 
  in 
  Castilla, 
  but 
  also 
  the 
  forms 
  of 
  the 
  leaves, 
  showing 
  that 
  the 
  

   vegetative 
  specializations 
  are 
  deep-seated 
  and 
  long-standing. 
  No 
  

   other 
  tree 
  has 
  afforded 
  more 
  outstanding 
  examples 
  of 
  vegetative 
  

   specialization 
  than 
  Castilla. 
  The 
  sexes 
  are 
  on 
  separate 
  trees, 
  the 
  in- 
  

   florescences 
  are 
  of 
  three 
  kinds, 
  the 
  branches 
  of 
  two 
  kinds, 
  and 
  the 
  

   leaves 
  of 
  four 
  kinds. 
  An 
  adaptive 
  advantage 
  of 
  the 
  specialized 
  

   branching 
  habits 
  is 
  seen 
  in 
  the 
  fact 
  that 
  Castilla 
  outgrows 
  the 
  Para 
  

   rubber 
  tree 
  in 
  the 
  early 
  stage 
  of 
  development, 
  before 
  fruiting 
  begins. 
  

   Instead 
  of 
  the 
  early 
  growth 
  being 
  limited 
  to 
  the 
  production 
  of 
  a 
  very 
  

   slender 
  trunk 
  as 
  in 
  the 
  Para 
  rubber 
  tree, 
  the 
  young 
  Castilla 
  trees 
  de- 
  

   velop 
  specialized 
  lateral 
  branches 
  and 
  soon 
  form 
  a 
  thicker 
  trunk 
  and 
  

   a 
  thicker 
  layer 
  of 
  latex-bearing 
  bark, 
  so 
  that 
  in 
  a 
  few 
  years 
  the 
  total 
  

   content 
  of 
  rubber 
  in 
  a 
  Castilla 
  tree 
  may 
  be 
  several 
  times 
  larger 
  than 
  in 
  

   a 
  Para 
  rubber 
  tree. 
  Illustrations 
  of 
  Castilla 
  trees, 
  showing 
  their 
  rapid 
  

   growth 
  and 
  peculiar 
  branching 
  habits, 
  were 
  published 
  in 
  1903. 
  

  

  