﻿392 
  ANNUAL 
  REPORT 
  SMITHSONIAN 
  INSTITUTION, 
  1943 
  

  

  and 
  thickening 
  the 
  tissues 
  of 
  the 
  leaves. 
  Such 
  adjustments 
  to 
  condi- 
  

   tions 
  are 
  shown 
  in 
  the 
  Para 
  rubber 
  tree, 
  but 
  to 
  a 
  rather 
  slight 
  extent. 
  

   Although 
  the 
  seedling 
  foliage 
  is 
  delicate, 
  exposure 
  to 
  the 
  sun 
  is 
  not 
  

   injurious 
  as 
  long 
  as 
  the 
  soil 
  and 
  the 
  air 
  conditions 
  do 
  not 
  reach 
  a 
  state 
  

   of 
  stress 
  or 
  injurious 
  shortage 
  of 
  moisture. 
  With 
  other 
  conditions 
  

   sufficiently 
  favorable, 
  more 
  growth 
  may 
  be 
  made 
  in 
  the 
  sun 
  than 
  in 
  

   the 
  shade, 
  but 
  the 
  manner 
  of 
  growing 
  is 
  the 
  same. 
  

  

  The 
  adaptive 
  specializations 
  of 
  the 
  Para 
  rubber 
  tree 
  offer 
  several 
  

   complete 
  contrasts 
  with 
  those 
  of 
  the 
  Castilla 
  tree. 
  The 
  number 
  of 
  

   specialized 
  features 
  is 
  nearly 
  as 
  great, 
  but 
  they 
  are 
  not 
  along 
  parallel 
  

   lines, 
  or 
  even 
  analogous. 
  Instead 
  of 
  developing 
  branches 
  3 
  or 
  4 
  feet 
  

   from 
  the 
  ground, 
  where 
  the 
  Castilla 
  tree 
  produces 
  its 
  longest 
  lateral 
  

   branches, 
  the 
  Para 
  rubber 
  tree 
  normally 
  produces 
  no 
  branches 
  at 
  all 
  

   to 
  a 
  height 
  of 
  12 
  to 
  20 
  feet. 
  The 
  suppression 
  of 
  all 
  branch-forming 
  

   buds 
  on 
  the 
  many 
  joints 
  or 
  sections 
  of 
  the 
  trunk 
  is 
  a 
  specialized 
  feature, 
  

   since 
  it 
  is 
  possible 
  for 
  branches 
  to 
  be 
  formed 
  at 
  any 
  height 
  if 
  the 
  

   trunk 
  is 
  cut 
  back. 
  Even 
  in 
  the 
  axils 
  of 
  the 
  cotyledons 
  are 
  buds 
  that 
  de- 
  

   velop 
  if 
  the 
  plumule 
  is 
  removed. 
  This 
  makes 
  it 
  possible 
  for 
  the 
  seed- 
  

   lings 
  to 
  be 
  split, 
  by 
  methods 
  described 
  and 
  illustrated 
  by 
  Loomis 
  in 
  

   1942, 
  and 
  two 
  plants 
  raised 
  from 
  the 
  same 
  seed. 
  

  

  The 
  habit 
  of 
  branching 
  in 
  the 
  Para 
  rubber 
  tree 
  is 
  consistent 
  with 
  the 
  

   habit 
  of 
  forming 
  the 
  leaves 
  in 
  clusters 
  or 
  "flushes." 
  Branching 
  be- 
  

   gins 
  abruptly, 
  with 
  several 
  vegetative 
  buds 
  developing 
  at 
  the 
  same 
  

   time 
  from 
  the 
  axils 
  of 
  several 
  leaves 
  of 
  the 
  same 
  whorl 
  or 
  cluster, 
  at 
  

   nearly 
  the 
  same 
  level. 
  The 
  formation 
  of 
  such 
  a 
  cluster 
  of 
  branches 
  

   normally 
  makes 
  an 
  end 
  of 
  the 
  main 
  trunk 
  of 
  the 
  tree. 
  In 
  exceptional 
  

   cases 
  only 
  two 
  or 
  three 
  branches 
  are 
  formed 
  in 
  the 
  first 
  whorl, 
  and 
  the 
  

   trunk 
  may 
  continue 
  its 
  upward 
  growth 
  until 
  more 
  branches 
  are 
  de- 
  

   veloped, 
  but 
  after 
  a 
  normal 
  whorl 
  of 
  6 
  to 
  12 
  branches 
  has 
  developed, 
  

   a 
  spreading 
  or 
  ascending 
  treetop 
  is 
  usually 
  formed, 
  with 
  no 
  indica- 
  

   tion 
  of 
  a 
  central 
  trunk. 
  A 
  brief 
  account 
  of 
  "Branching 
  Habits 
  of 
  the 
  

   Hevea 
  Rubber 
  Tree," 
  explaining 
  their 
  cultural 
  significance, 
  was 
  pub- 
  

   lished 
  in 
  1930. 
  

  

  The 
  earlier 
  fruiting 
  of 
  the 
  Castilla 
  tree 
  is 
  determined 
  by 
  the 
  habits 
  

   of 
  branching. 
  Although 
  the 
  lowest 
  branches 
  of 
  Castilla 
  usually 
  

   have 
  no 
  flowers 
  or 
  fruits, 
  they 
  are 
  of 
  the 
  fruiting 
  type, 
  and 
  the 
  func- 
  

   tional 
  fruiting 
  stage 
  is 
  soon 
  reached, 
  as 
  in 
  plate 
  2, 
  often 
  within 
  5 
  or 
  6 
  

   feet 
  from 
  the 
  ground. 
  At 
  the 
  corresponding 
  stage 
  of 
  growth 
  the 
  

   Para 
  rubber 
  tree 
  has 
  only 
  half 
  completed 
  the 
  development 
  of 
  its 
  

   primary 
  upright 
  as 
  a 
  simple, 
  straight 
  rod, 
  normally 
  without 
  the 
  few 
  

   branches 
  shown 
  at 
  the 
  right 
  in 
  plate 
  11. 
  The 
  uniform 
  suppression 
  

   of 
  branches 
  on 
  the 
  many 
  trunk 
  sections 
  that 
  form 
  the 
  primary 
  up- 
  

   right 
  of 
  the 
  Para 
  rubber 
  tree 
  is 
  therefore 
  to 
  be 
  considered 
  as 
  a 
  special- 
  

   ized 
  feature 
  of 
  adaptation 
  to 
  forest 
  conditions. 
  The 
  numerous 
  differ- 
  

  

  