﻿FLOWERS 
  

  

  129 
  

  

  119. 
  Symmetry 
  of 
  the 
  flower. 
  Except 
  in 
  a 
  comparatively 
  

   small 
  number 
  of 
  cases 
  (of 
  which 
  the 
  familiar 
  canna, 
  or 
  Indian 
  

   shot, 
  is 
  a 
  good 
  example) 
  the 
  perianth 
  usually 
  shows 
  some 
  

   kind 
  of 
  symmetry. 
  Either 
  (as 
  in 
  fig. 
  102) 
  the 
  parts 
  are 
  ar- 
  

   ranged 
  in 
  a 
  radial 
  fashion, 
  like 
  the 
  points 
  of 
  a 
  star, 
  or 
  else 
  

   they 
  have 
  corresponding 
  halves 
  

  

  in 
  one 
  plane 
  to 
  the 
  right 
  and 
  

   left 
  of 
  an 
  axial 
  line, 
  as 
  in 
  pan- 
  

   sies 
  and 
  violets 
  (fig. 
  100), 
  in 
  the 
  

   most 
  familiar 
  flowers 
  of 
  the 
  Pea 
  

   family, 
  and 
  in 
  those 
  of 
  the 
  Mint 
  

   family. 
  Flowers 
  with 
  radial 
  

   symmetry 
  are 
  said 
  -to 
  be 
  actino- 
  

   morphic, 
  and 
  those 
  with 
  corre- 
  

   sponding 
  halves 
  are 
  said 
  to 
  

   have 
  bilateral 
  symmetry, 
  or 
  to 
  

   be 
  zygomorpltic. 
  

  

  Sometimes, 
  as 
  in 
  the 
  Milk- 
  

   weed 
  family, 
  the 
  corolla 
  has 
  

   extraordinary 
  forms 
  which 
  fa- 
  

   cilitate 
  seed 
  production 
  by 
  the 
  

   aid 
  of 
  insect 
  visitors 
  (fig. 
  134). 
  

  

  120. 
  Parts 
  of 
  the 
  stamen 
  ; 
  

   union 
  of 
  stamens. 
  Many 
  stamens 
  

   have 
  a 
  form 
  similar 
  to 
  that 
  shown 
  

   in 
  figure 
  107, 
  A, 
  consisting 
  of 
  a 
  

   rather 
  slender 
  stalk 
  (the 
  filament*) 
  

   which 
  bears 
  a 
  stouter 
  structure, 
  

  

  the 
  anther. 
  Anthers 
  which 
  have 
  no 
  filaments 
  are 
  said 
  to 
  be 
  

   sessile. 
  Within 
  the 
  anther 
  the 
  stamen 
  produces 
  a 
  powdery 
  or 
  

   pasty 
  substance 
  known 
  as 
  pollen, 
  which, 
  when 
  magnified, 
  is 
  

   seen 
  to 
  consist 
  of 
  minute 
  grains 
  (fig. 
  117). 
  These 
  differ 
  

   greatly 
  in 
  form 
  and 
  markings 
  in 
  different 
  families 
  of 
  plants. 
  

   The 
  mode 
  of 
  origin 
  of 
  the 
  pollen 
  sacs 
  in 
  which 
  pollen 
  is 
  pro- 
  

   duced 
  is 
  partially 
  shown 
  in 
  figure 
  108. 
  When 
  the 
  sacs 
  are 
  

   fully 
  mature, 
  they 
  open 
  and 
  allow 
  their 
  contents 
  to 
  escape. 
  

  

  > 
  1 
  

  

  FIG. 
  108. 
  Diagrams 
  to 
  show 
  struc- 
  

   ture 
  of 
  an 
  anther 
  

  

  A, 
  younger 
  stage, 
  \vith 
  four 
  cham- 
  

   bers, 
  or 
  loculcs 
  (loc), 
  containing 
  pollen 
  

   mother 
  cells 
  dividing 
  to 
  form 
  pollen 
  

   grains 
  ; 
  B, 
  an 
  older 
  stage, 
  in 
  which 
  the 
  

   pollen 
  grains 
  (p) 
  are 
  fully 
  formed 
  and 
  

   each 
  pair 
  of 
  locules 
  is 
  uniting 
  to 
  form 
  a 
  

   pollen 
  sac, 
  which 
  will 
  split 
  open 
  and 
  dis- 
  

   charge 
  along 
  the 
  line 
  of 
  dehiscence 
  ('/). 
  

   After 
  Baillon 
  and 
  Luerssen 
  

  

  