﻿364 
  ANNUAL 
  REPORT 
  SMITHSONIAN 
  INSTITUTION, 
  1943 
  

  

  Page 
  

  

  A 
  growth 
  disorder 
  in 
  seedlings 
  of 
  Para 
  rubber 
  396 
  

  

  Diversity 
  in 
  abnormal 
  plants 
  397 
  

  

  Recovery 
  of 
  normal 
  leaf 
  forms 
  397 
  

  

  A 
  mature 
  tree 
  with 
  narrow 
  leaves 
  398 
  

  

  The 
  Para 
  rubber 
  tree 
  as 
  a 
  hybrid 
  stock 
  398 
  

  

  Rubber 
  in 
  a 
  desert 
  shrub 
  398 
  

  

  Developing 
  a 
  guayule 
  industry 
  400 
  

  

  Effect 
  of 
  Ridley's 
  discovery 
  on 
  guayule 
  and 
  Castilla 
  400 
  

  

  Possibility 
  of 
  applying 
  guayule 
  extraction 
  methods 
  to 
  Castilla 
  401 
  

  

  Rubber 
  in 
  desert 
  milkweeds 
  402 
  

  

  Cryptostegia 
  as 
  a 
  soil 
  cover 
  403 
  

  

  The 
  African 
  rubber 
  tree 
  in 
  shelter 
  belts 
  404 
  

  

  A 
  hardy 
  gutta-percha 
  tree 
  404 
  

  

  Eucommia, 
  a 
  tree 
  that 
  never 
  blossoms 
  405 
  

  

  Eucommia 
  suppresses 
  all 
  terminal 
  buds 
  406 
  

  

  The 
  balata 
  tree 
  407 
  

  

  The 
  sapodilla, 
  or 
  chewing-gum 
  tree 
  408 
  

  

  Our 
  household 
  "rubber 
  plant" 
  409 
  

  

  Two 
  rubbers 
  in 
  one 
  tree 
  409 
  

  

  Taking 
  account 
  of 
  natural 
  sources 
  of 
  rubber 
  is 
  a 
  scientific 
  task 
  of 
  

   enormous 
  proportions, 
  which 
  as 
  yet 
  has 
  received 
  only 
  casual 
  and 
  inter- 
  

   mittent 
  attention. 
  Only 
  a 
  few 
  species 
  have 
  been 
  studied 
  and 
  evaluated, 
  

   while 
  thousands 
  are 
  known 
  to 
  contain 
  rubber, 
  and 
  other 
  thousands 
  

   doubtless 
  remain 
  to 
  be 
  discovered. 
  Rubber 
  and 
  rubberlike 
  substances 
  

   are 
  not 
  restricted 
  to 
  plants 
  that 
  have 
  latex, 
  the 
  milky 
  juice 
  that 
  is 
  car- 
  

   ried 
  in 
  minute 
  tubes 
  apart 
  from 
  the 
  other 
  tissues. 
  Latex 
  may 
  have 
  

   functions 
  in 
  the 
  plant 
  economy 
  other 
  than 
  the 
  storage 
  or 
  transfer 
  

   of 
  the 
  rubber-forming 
  material, 
  but 
  nothing 
  has 
  been 
  found 
  to 
  indi- 
  

   cate 
  that 
  the 
  rubber 
  material 
  itself 
  is 
  more 
  than 
  a 
  waste 
  product, 
  like 
  

   the 
  resins, 
  tannins, 
  or 
  lignins 
  that 
  are 
  formed 
  in 
  the 
  various 
  groups 
  of 
  

   higher 
  plants. 
  Thus 
  no 
  biological 
  limit 
  can 
  be 
  set 
  to 
  the 
  need 
  of 
  a 
  

   general 
  survey 
  of 
  the 
  plant 
  kingdom. 
  

  

  A 
  beginning 
  of 
  the 
  search 
  for 
  rubber 
  resources 
  may 
  be 
  reckoned 
  

   from 
  a 
  century 
  ago, 
  when 
  the 
  Para 
  rubber 
  tree 
  in 
  the 
  forest 
  of 
  the 
  

   Amazon 
  valley 
  began 
  to 
  be 
  exploited 
  on 
  a 
  large 
  scale, 
  after 
  the 
  Castilla 
  

   or 
  Central 
  American 
  rubber 
  tree, 
  the 
  original 
  source 
  of 
  commercial 
  

   rubber, 
  was 
  largely 
  exhausted. 
  To 
  the 
  middle 
  of 
  the 
  last 
  century 
  most 
  

   of 
  the 
  rubber 
  had 
  been 
  obtained 
  from 
  the 
  Castilla 
  tree, 
  and 
  Brazil 
  has 
  

   continued 
  to 
  furnish 
  Castilla 
  rubber 
  from 
  the 
  more 
  remote 
  or 
  less 
  

   accessible 
  districts. 
  The 
  Castilla 
  rubber 
  is 
  handled 
  in 
  Brazil 
  under 
  the 
  

   name 
  caucho, 
  while 
  the 
  Para 
  rubber 
  is 
  known 
  as 
  borracha. 
  The 
  com- 
  

   mercial 
  preponderance 
  of 
  the 
  Para 
  rubber 
  in 
  recent 
  decades 
  has 
  left 
  

   the 
  Castilla 
  rubber 
  in 
  such 
  obscurity 
  — 
  or 
  even 
  oblivion 
  — 
  that 
  popular 
  

   writers 
  were 
  led 
  to 
  suppose 
  that 
  the 
  history 
  of 
  rubber 
  began 
  in 
  the 
  

   Amazon 
  valley. 
  In 
  reality 
  the 
  Castilla 
  rubber 
  had 
  been 
  known 
  in 
  

   Mexico 
  and 
  elsewhere 
  in 
  tropical 
  America 
  for 
  more 
  than 
  three 
  cen- 
  

   turies 
  before 
  the 
  Para 
  rubber 
  became 
  prominent. 
  

  

  