﻿396 
  ANNUAL 
  REPORT 
  SMITHSONIAN 
  INSTITUTION, 
  1943 
  

  

  tree. 
  The 
  seedling 
  leaves 
  are 
  much 
  thinner 
  than 
  those 
  of 
  adult 
  trees, 
  

   and 
  apparently 
  much 
  more 
  susceptible 
  to 
  injury 
  from 
  exposure 
  to 
  

   adverse 
  conditions. 
  The 
  change 
  in 
  texture 
  from 
  the 
  thin 
  seedling 
  

   leaves 
  to 
  the 
  thicker 
  and 
  firmer 
  adult 
  leaves 
  occurs 
  much 
  earlier 
  in 
  

   some 
  trees 
  than 
  in 
  others, 
  a 
  difference 
  that 
  may 
  be 
  of 
  value 
  in 
  develop- 
  

   ing 
  resistant 
  varieties. 
  

  

  Where 
  soil 
  conditions 
  are 
  perfect, 
  seedling 
  plants 
  may 
  tolerate 
  full 
  

   exposure, 
  but 
  in 
  heavier 
  soils 
  the 
  seedlings 
  are 
  more 
  susceptible 
  to 
  in- 
  

   jury 
  from 
  direct 
  sunlight. 
  Under 
  the 
  equable 
  forest 
  conditions 
  the 
  

   seedlings 
  have 
  a 
  persistent 
  vitality 
  that 
  probably 
  allows 
  them 
  to 
  

   survive 
  for 
  many 
  years 
  in 
  places 
  that 
  are 
  too 
  dark 
  or 
  too 
  unfavorable 
  

   m 
  other 
  ways 
  to 
  permit 
  normal 
  growth. 
  Plants 
  abandoned 
  in 
  old 
  

   seed 
  beds, 
  after 
  being 
  stunted 
  for 
  2 
  or 
  3 
  years, 
  have 
  been 
  able 
  to^re- 
  

   cover 
  the 
  vigor 
  of 
  normal 
  plants. 
  The 
  tolerance 
  of 
  shade 
  conditions 
  

   shows 
  the 
  extent 
  of 
  forest 
  adaptation, 
  which 
  also 
  may 
  be 
  inferred 
  

   from 
  the 
  absence 
  of 
  surface 
  protection 
  by 
  hairs 
  or 
  bud 
  scales 
  as 
  in 
  

   Castilla, 
  and 
  from 
  the 
  presence 
  of 
  special 
  openings 
  or 
  water 
  pores 
  in 
  

   the 
  lower 
  surface 
  of 
  the 
  leaves, 
  as 
  described 
  by 
  Bobilioff. 
  

  

  A 
  GROWTH 
  DISORDER 
  IN 
  SEEDLINGS 
  OF 
  PARA 
  RUBBER 
  

  

  A 
  growth 
  disorder 
  often 
  affecting 
  large 
  proportions 
  of 
  the 
  seedlings 
  

   of 
  the 
  Para 
  rubber 
  tree 
  is 
  worthy 
  of 
  careful 
  study 
  and 
  comparison 
  

   with 
  analogous 
  disorders 
  of 
  other 
  plants, 
  in 
  the 
  interest 
  of 
  better 
  

   understanding 
  of 
  habits 
  of 
  growth 
  and 
  cultural 
  requirements 
  during 
  

   the 
  seedling 
  and 
  juvenile 
  stages. 
  Since 
  the 
  disorder 
  is 
  most 
  severe 
  

   and 
  striking 
  in 
  the 
  young 
  seedlings, 
  much 
  of 
  the 
  injury 
  has 
  been 
  

   avoided 
  by 
  the 
  simple 
  expedient 
  of 
  discarding 
  all 
  the 
  stunted 
  or 
  dis- 
  

   torted 
  individuals 
  in 
  the 
  nursery 
  stocks, 
  under 
  the 
  usual 
  precaution 
  

   that 
  only 
  normal, 
  vigorous 
  trees 
  are 
  to 
  be 
  set 
  in 
  the 
  plantations. 
  Even 
  

   among 
  normal 
  rubber 
  trees, 
  those 
  that 
  pass 
  muster 
  in 
  transplanting 
  

   and 
  make 
  satisfactory 
  growth 
  in 
  the 
  plantations, 
  an 
  enormous 
  di- 
  

   versity 
  is 
  found 
  — 
  greater 
  than 
  in 
  other 
  tree 
  crops. 
  

  

  The 
  trees 
  in 
  the 
  rubber 
  plantations 
  are 
  found 
  to 
  differ 
  not 
  only 
  in 
  

   the 
  stature 
  and 
  proportions 
  of 
  the 
  trunks, 
  leaves, 
  floral 
  characters, 
  and 
  

   seeds, 
  but 
  also 
  in 
  the 
  bark 
  texture 
  and 
  in 
  the 
  latex 
  tubes, 
  which 
  more 
  

   definitely 
  affect 
  the 
  yields 
  of 
  rubber. 
  The 
  surface 
  of 
  the 
  bark 
  may 
  be 
  

   smooth 
  or 
  finely 
  wrinkled 
  like 
  a 
  beech 
  tree, 
  or 
  rough 
  and 
  remose 
  like 
  

   an 
  elm 
  or 
  an 
  oak, 
  while 
  the 
  structure 
  may 
  be 
  uniform, 
  soft 
  and 
  cheesy, 
  

   or 
  brittle 
  and 
  gritty 
  with 
  stone 
  cells. 
  In 
  experiments 
  where 
  records 
  

   of 
  individual 
  trees 
  are 
  carried 
  through 
  long 
  periods 
  some 
  trees 
  are 
  

   found 
  to 
  be 
  yielding 
  scarcely 
  any 
  rubber, 
  and 
  others 
  only 
  small 
  

   amounts, 
  while 
  a 
  few 
  individuals 
  are 
  far 
  above 
  the 
  general 
  average, 
  

   so 
  that 
  75 
  percent 
  of 
  the 
  rubber 
  is 
  produced 
  by 
  15 
  to 
  25 
  percent 
  of 
  the 
  

   trees. 
  Budding 
  from 
  high-yielding 
  trees 
  raises 
  the 
  average, 
  although 
  

  

  