﻿394 
  ANNUAL 
  REPORT 
  SMITHSONIAN 
  INSTITUTION, 
  1943 
  

  

  ing 
  maturity 
  may 
  depend 
  very 
  acutely 
  upon 
  the 
  ability 
  of 
  the 
  plant 
  

   to 
  take 
  full 
  advantage 
  of 
  the 
  light 
  that 
  reaches 
  it. 
  The 
  danger 
  of 
  

   the 
  young 
  plant 
  losing 
  any 
  light 
  by 
  shading 
  its 
  own 
  leaves 
  is 
  avoided 
  

   by 
  the 
  arrangement 
  of 
  the 
  leaves 
  in 
  rosettes, 
  forming 
  a 
  circular 
  

   cluster 
  at 
  the 
  end 
  of 
  the 
  shoot, 
  like 
  a 
  small 
  umbrella. 
  

  

  LEAVES 
  ARRANGED 
  IN 
  ROSETTES 
  

  

  The 
  leaves 
  that 
  form 
  a 
  rosette 
  are 
  of 
  different 
  sizes 
  and 
  have 
  

   petioles 
  of 
  different 
  lengths, 
  so 
  that 
  the 
  rosette 
  arrangement 
  gives 
  

   them 
  full 
  exposure 
  to 
  the 
  light. 
  The 
  complete 
  suppression 
  of 
  the 
  

   leaves 
  on 
  the 
  lower 
  joints 
  of 
  each 
  of 
  the 
  growth 
  sections 
  — 
  the 
  leaves 
  

   that 
  would 
  be 
  shaded 
  by 
  the 
  terminal 
  rosette 
  — 
  is 
  another 
  feature 
  of 
  

   the 
  arrangement. 
  The 
  leafless 
  lower 
  joints 
  add 
  notably 
  to 
  the 
  length 
  

   of 
  the 
  section 
  and 
  contribute 
  to 
  the 
  height 
  of 
  the 
  young 
  tree. 
  With 
  

   every 
  section 
  that 
  is 
  added 
  the 
  light 
  conditions 
  are 
  improved 
  and 
  the 
  

   tree's 
  chances 
  are 
  increased 
  of 
  emerging 
  eventually 
  through 
  the 
  roof 
  

   of 
  the 
  forest 
  and 
  finding 
  a 
  place 
  in 
  the 
  sun. 
  

  

  The 
  number 
  of 
  leaves 
  in 
  a 
  rosette 
  is 
  increased 
  rapidly 
  in 
  the 
  suc- 
  

   cessive 
  sections 
  that 
  are 
  formed, 
  from 
  the 
  2 
  leaves 
  of 
  the 
  first 
  stage 
  

   of 
  the 
  seedlings 
  to 
  12 
  or 
  15 
  leaves. 
  Vigorous 
  plants 
  in 
  the 
  second 
  

   and 
  third 
  seasons 
  may 
  have 
  from 
  20 
  to 
  30 
  leaves 
  in 
  a 
  rosette, 
  while 
  

   5 
  or 
  6 
  of 
  the 
  lower 
  joints 
  of 
  the 
  growth 
  section 
  are 
  without 
  leaves. 
  

  

  MANY 
  LEAFLESS 
  MET 
  AIMERS 
  

  

  A 
  further 
  specialization 
  for 
  forest 
  conditions 
  is 
  seen 
  in 
  the 
  suppres- 
  

   sion 
  of 
  the 
  leaves 
  on 
  many 
  of 
  the 
  metamers, 
  the 
  structural 
  units 
  that 
  

   make 
  up 
  the 
  trunk 
  of 
  the 
  Para 
  rubber 
  tree. 
  The 
  first 
  stage 
  of 
  the 
  

   seedling 
  is 
  highly 
  specialized 
  in 
  this 
  respect, 
  with 
  basal 
  joint 
  or 
  

   epicotyl, 
  the 
  first 
  trunk 
  section 
  above 
  the 
  cotyledons, 
  not 
  bearing 
  

   leaves, 
  although 
  remarkably 
  elongate. 
  Epicotyls 
  measuring 
  9 
  to 
  14 
  

   inches 
  in 
  length 
  were 
  noted 
  in 
  Haiti. 
  The 
  Castilla 
  epicotyl 
  ends 
  with 
  

   a 
  pair 
  of 
  leaves, 
  as 
  shown 
  in 
  plate 
  6, 
  while 
  that 
  of 
  the 
  Para 
  rubber 
  

   tree 
  has 
  the 
  leaves 
  suppressed, 
  and 
  two 
  or 
  three 
  shorter 
  leafless 
  meta- 
  

   mers 
  may 
  be 
  formed 
  above 
  the 
  epicotyl, 
  below 
  the 
  first 
  pair 
  of 
  leaves. 
  

  

  The 
  long 
  epicotyl 
  and 
  adjacent 
  leafless 
  metamers 
  of 
  the 
  Para 
  rub- 
  

   ber 
  seedlings, 
  shown 
  in 
  plates 
  7 
  and 
  8, 
  carry 
  the 
  first 
  leaves 
  often 
  a 
  

   foot 
  or 
  more 
  above 
  the 
  ground, 
  much 
  higher 
  than 
  the 
  short 
  epicotyl 
  

   of 
  Castilla, 
  shown 
  in 
  natural 
  size 
  in 
  plate 
  6. 
  Thus 
  it 
  may 
  be 
  said 
  that 
  

   the 
  seedlings 
  of 
  the 
  Para 
  rubber 
  tree 
  have 
  all 
  the 
  leaves 
  suppressed 
  

   in 
  the 
  lower 
  stem 
  sections 
  corresponding 
  to 
  those 
  of 
  Castilla 
  shown 
  

   in 
  plate 
  6, 
  where 
  all 
  the 
  metamers 
  bear 
  leaves. 
  

  

  As 
  seen 
  in 
  plates 
  7 
  and 
  8, 
  the 
  first 
  two 
  leaves 
  of 
  the 
  Para 
  rubber 
  

   seedlings 
  are 
  borne 
  at 
  nearly 
  the 
  same 
  level, 
  while 
  the 
  next 
  leaf 
  above 
  

   this 
  first 
  pair 
  usually 
  stands 
  alone 
  at 
  the 
  end, 
  above 
  an 
  intervening 
  

  

  