﻿The 
  Vegetative 
  Morphology 
  of 
  Pistia 
  and 
  the 
  Lemnacece. 
  101 
  

  

  panying 
  figures, 
  that 
  my 
  observations 
  conflict 
  with 
  those 
  of 
  Engler, 
  who 
  

   regards 
  the 
  bud 
  as 
  occupying 
  an 
  anomalous 
  position 
  outside 
  the 
  sheath. 
  I 
  am 
  

   also 
  unable 
  to 
  confirm 
  Velenovskys* 
  statement 
  that 
  the 
  buds 
  are 
  originally 
  

   median, 
  but 
  are 
  forced 
  by 
  pressure 
  to 
  occupy 
  a 
  lateral 
  position 
  ; 
  they 
  are 
  

   undoubtedly, 
  from 
  the 
  first, 
  completely 
  lateral 
  to 
  the 
  limb, 
  though 
  lying 
  

   inside 
  the 
  sheath. 
  

  

  The 
  Comparison 
  of 
  Pistia 
  and 
  Spirodela. 
  

  

  The 
  interest 
  of 
  the 
  points 
  in 
  which 
  my 
  results 
  conflict 
  with 
  those 
  of 
  Engler 
  

   and 
  Velenovsky, 
  lies 
  in 
  the 
  fact 
  that, 
  in 
  every 
  case 
  in 
  which 
  I 
  differ 
  from 
  

   these 
  two 
  writers, 
  my 
  results 
  point 
  to 
  an 
  even 
  closer 
  morphological 
  relation 
  

   between 
  Pistia 
  and 
  the 
  Lemnacete 
  than 
  has 
  been 
  hitherto 
  claimed. 
  It 
  seems 
  

   clear 
  that 
  the 
  lateral 
  bud-containing 
  pockets 
  formed 
  by 
  the 
  sheath 
  of 
  Pistia 
  

   are 
  exactly 
  equivalent 
  to 
  the 
  pockets 
  of 
  the 
  Leinnacese. 
  The 
  sketch 
  of 
  a 
  

   Spirodela 
  plant 
  seen 
  from 
  below 
  (fig. 
  8) 
  will 
  perhaps 
  help 
  to 
  explain 
  this 
  

  

  Fig. 
  8. 
  — 
  Spirodela 
  polyrrhiza, 
  Schleid. 
  A 
  plant 
  viewed 
  from 
  the 
  underside 
  (enlarged) 
  ; 
  

   I., 
  limb 
  of 
  leaf 
  belonging 
  to 
  main 
  axis, 
  ax. 
  ; 
  r., 
  roots 
  (cut 
  short) 
  ; 
  p. 
  and 
  p'., 
  pockets 
  

   between 
  wings 
  of 
  sheath 
  (s. 
  and 
  s'.) 
  and 
  axis, 
  enclosing 
  buds,, 
  b. 
  and 
  b'. 
  ; 
  /. 
  and/'., 
  

   ligular 
  flaps 
  of 
  sheath. 
  

  

  relation. 
  The 
  petiolar 
  phyllode, 
  I, 
  passes 
  at 
  its 
  base 
  into 
  the 
  reduced 
  and 
  

   flattened 
  axis, 
  ax., 
  of 
  which 
  it 
  forms 
  the 
  apparent 
  continuation, 
  exactly 
  as 
  the 
  

   spathe 
  of 
  Acorus 
  continues 
  down 
  into 
  the 
  scape, 
  but 
  with 
  the 
  difference 
  that 
  

   in 
  Spirodela 
  the 
  growing 
  point 
  of 
  the 
  axis 
  completely 
  aborts, 
  whereas 
  in 
  the 
  

   fertile 
  shoot 
  of 
  Acorus 
  it 
  forms 
  the 
  spadix. 
  Just 
  where 
  the 
  limb 
  of 
  the 
  duck- 
  

   weed 
  frond 
  fuses 
  with 
  the 
  axis, 
  a 
  group 
  of 
  roots, 
  r., 
  takes 
  its 
  origin. 
  We 
  find 
  

   an 
  analogy 
  to 
  this 
  in 
  Pistia, 
  where 
  fig. 
  4 
  shows 
  roots 
  arising 
  from 
  the 
  base 
  of 
  

   the 
  limb 
  of 
  leaf 
  2, 
  at 
  the 
  level 
  of 
  its 
  junction 
  with 
  the 
  axis. 
  The 
  two 
  wings 
  

   of 
  the 
  sheath 
  of 
  Spirodela, 
  s 
  and 
  s' 
  , 
  are 
  developed, 
  just 
  as 
  in 
  Pistia,, 
  below 
  the 
  

   attachment 
  of 
  the 
  limb 
  to 
  the 
  axis. 
  They 
  do 
  not 
  meet 
  and 
  fuse 
  into 
  a 
  

  

  * 
  Velenovsky, 
  J. 
  (1907). 
  

  

  H 
  2 
  

  

  