﻿402 
  ANNUAL 
  REPORT 
  SMITHSONIAN 
  INSTITUTION, 
  1943 
  

  

  is 
  without 
  foundation. 
  The 
  latex 
  tubes 
  are 
  only 
  slightly 
  compressed 
  

   by 
  the 
  release 
  of 
  the 
  bark 
  pressure 
  and 
  are 
  still 
  full 
  of 
  latex, 
  which 
  

   remains 
  in 
  the 
  bark 
  and 
  is 
  lost. 
  The 
  proportion 
  of 
  rubber 
  to 
  bark 
  

   tissue 
  in 
  Castilla 
  is 
  doubtless 
  much 
  lower 
  than 
  in 
  guayule, 
  since 
  the 
  

   Castilla 
  bark 
  is 
  woody 
  and 
  fibrous, 
  but 
  with 
  the 
  rubber 
  coagulated 
  in 
  

   tough 
  elastic 
  strands, 
  the 
  extraction 
  process 
  may 
  be 
  much 
  simpler. 
  

   Guayule 
  must 
  be 
  ground 
  very 
  fine, 
  to 
  the 
  point 
  of 
  breaking 
  down 
  

   individual 
  cells, 
  in 
  order 
  to 
  release 
  the 
  rubber 
  material. 
  

  

  Several 
  cultural 
  advantages 
  of 
  Castilla 
  are 
  obvious. 
  The 
  seedlings 
  

   and 
  young 
  plants 
  are 
  hardier 
  than 
  those 
  of 
  the 
  Para 
  rubber 
  tree, 
  in 
  

   the 
  sense 
  of 
  being 
  adapted 
  to 
  a 
  much 
  wider 
  range 
  of 
  adverse 
  con- 
  

   ditions. 
  The 
  young 
  trees 
  develop 
  and 
  reproduce 
  more 
  rapidly, 
  and 
  

   also 
  propagate 
  readily 
  from 
  large 
  cuttings 
  of 
  the 
  vegetative 
  branches. 
  

   Thus 
  it 
  may 
  be 
  hoped 
  that 
  the 
  renewal 
  of 
  interest 
  in 
  Castilla 
  and 
  

   guayule 
  during 
  the 
  present 
  wartime 
  emergency 
  will 
  carry 
  through 
  to 
  

   an 
  effective 
  determination 
  of 
  production 
  possiblities. 
  

  

  Not 
  only 
  the 
  Castilla 
  rubber 
  tree, 
  but 
  other 
  latex 
  trees 
  with 
  similar 
  

   tapping 
  problems, 
  such 
  as 
  Ficus 
  elastica, 
  chicle, 
  and 
  balata, 
  are 
  of 
  

   interest 
  from 
  the 
  standpoint 
  of 
  mechanical 
  extraction. 
  It 
  is 
  not 
  

   unthinkable 
  that 
  trees 
  adapted 
  to 
  mechanical 
  extraction 
  eventually 
  

   might 
  replace 
  the 
  Para 
  rubber 
  and 
  lend 
  a 
  wider 
  significance 
  to 
  the 
  

   work 
  done 
  on 
  guayule. 
  A 
  man 
  of 
  great 
  energy, 
  acute 
  intelligence, 
  and 
  

   constructive 
  engineering 
  ability, 
  the 
  late 
  George 
  H. 
  Carnahan, 
  presi- 
  

   dent 
  for 
  many 
  years 
  of 
  the 
  Inter-Continental 
  Kubber 
  Company, 
  was 
  

   largely 
  responsible 
  for 
  the 
  remarkably 
  persistent 
  and 
  effective 
  in- 
  

   vestigation 
  of 
  the 
  cultural 
  and 
  mechanical 
  problems. 
  Unlike 
  many 
  

   private 
  undertakings 
  in 
  the 
  scientific 
  field, 
  detailed 
  accounts 
  of 
  var- 
  

   ious 
  stages 
  of 
  progress 
  in 
  the 
  guayule 
  undertaking 
  were 
  published. 
  

   Carnahan 
  undoubtedly 
  should 
  rank 
  with 
  Edison, 
  Kidley, 
  Wickham, 
  

   Goodyear, 
  Faraday, 
  and 
  La 
  Condamine 
  among 
  eminent 
  names 
  in 
  

   rubber. 
  

  

  RUBBER 
  IN 
  DESERT 
  MILKWEEDS 
  

  

  A 
  specialized 
  milkweed, 
  Asclepias 
  subulata, 
  adapted 
  to 
  extreme 
  con- 
  

   ditions 
  in 
  the 
  open 
  deserts 
  of 
  southern 
  California 
  and 
  Arizona, 
  was 
  

   studied 
  for 
  several 
  years 
  from 
  the 
  standpoint 
  of 
  utilization 
  as 
  a 
  field 
  

   crop, 
  and 
  a 
  report 
  was 
  published 
  in 
  1935. 
  The 
  rubber-bearing 
  stems 
  

   are 
  simple 
  and 
  straight 
  like 
  grass 
  stalks, 
  forming 
  upright 
  tufts 
  3 
  or 
  

   4 
  feet 
  tall. 
  The 
  leaves 
  are 
  only 
  rudimentary, 
  hardly 
  wider 
  than 
  pine 
  

   needles, 
  and 
  soon 
  fall 
  off. 
  The 
  upper 
  figure 
  of 
  plate 
  14 
  shows 
  the 
  

   habit 
  of 
  the 
  wild 
  plants 
  growing 
  in 
  a 
  cactus 
  desert 
  near 
  Superior, 
  

   Ariz. 
  The 
  plants 
  grow 
  readily 
  from 
  seeds 
  and 
  form 
  abundant 
  shoots 
  

   from 
  rootstocks 
  creeping 
  below 
  the 
  surface 
  of 
  the 
  soil, 
  as 
  shown 
  in 
  

   natural 
  size 
  in 
  the 
  left-hand 
  lower 
  figure 
  of 
  plate 
  14. 
  The 
  right-hand 
  

  

  