﻿148 
  

  

  INTRODUCTION 
  TO 
  BOTANY 
  

  

  then 
  reach 
  the 
  mature 
  pistillate 
  flowers 
  which 
  they 
  pollinate. 
  

   On 
  attempting 
  to 
  fly 
  out 
  of 
  the 
  flower 
  chamber 
  they 
  find 
  it 
  

   impossible 
  to 
  get 
  through 
  the 
  fringe 
  of 
  hairs. 
  After 
  a 
  time 
  

   (often 
  a 
  few 
  davs) 
  the 
  stigmas 
  wither, 
  and 
  in 
  place 
  of 
  each 
  a 
  

   drop 
  of 
  nectar 
  appears, 
  on 
  which 
  the 
  insects 
  feed. 
  At 
  length 
  

   the 
  staminate 
  flowers 
  mature 
  and 
  allow 
  a 
  considerable 
  quan- 
  

   tity 
  of 
  pollen 
  to 
  fall 
  to 
  the 
  

   bottom 
  of 
  the 
  chamber. 
  

   The 
  insects 
  crawl 
  about 
  

   in 
  this, 
  become 
  thoroughly 
  

   dusted 
  with 
  it, 
  and 
  finally, 
  

   as 
  the 
  palisade 
  hairs 
  wither 
  

   and 
  droop, 
  escape 
  and 
  fly 
  

   away 
  to 
  another 
  bl< 
  >ss< 
  miing 
  

   arum 
  plant, 
  and 
  cross-polli- 
  

   nate 
  its 
  flowers 
  in 
  turn. 
  The 
  

   number 
  of 
  insect 
  visitors 
  to 
  

   a 
  single 
  flower 
  cluster 
  is 
  

  

  O 
  

  

  enormous, 
  about 
  four 
  thou- 
  

   sand 
  midges 
  being 
  found 
  

   ill 
  one 
  flower 
  chamber. 
  

  

  140. 
  The 
  milkweed 
  ; 
  a 
  

   pinch-trap 
  flower. 
  The 
  milk- 
  

   weeds 
  1 
  are 
  admirable 
  in- 
  

   stances 
  of 
  what 
  are 
  called 
  

   pinch-trap 
  flowers. 
  There 
  

   are 
  more 
  than 
  twenty 
  kinds 
  of 
  milkweed 
  in 
  the 
  central 
  and 
  

   northeastern 
  states, 
  the 
  commonest 
  in 
  many 
  portions 
  of 
  the 
  

   country 
  being 
  the 
  one 
  shown 
  in 
  figure 
  133. 
  The 
  flowers, 
  of 
  

   peculiar 
  form 
  (fig. 
  134, 
  A), 
  are 
  borne 
  in 
  clusters. 
  The 
  general 
  

   structure 
  of 
  the 
  flower 
  can 
  be 
  understood 
  from 
  figure 
  134, 
  

   A 
  and 
  B. 
  The 
  detail 
  of 
  its 
  structure 
  that 
  is 
  of 
  most 
  inter- 
  

   est 
  in 
  the 
  study 
  of 
  modes 
  of 
  pollination 
  is 
  the 
  way 
  in 
  which 
  

   the 
  pollen 
  is 
  borne. 
  Each 
  of 
  the 
  five 
  anthers 
  produces 
  two 
  

   rather 
  large 
  pollen 
  masses. 
  Between 
  each 
  pair 
  of 
  anthers 
  is 
  

  

  1 
  Asclepias 
  and 
  Aceratea. 
  

  

  FIG. 
  133. 
  The 
  common 
  milkweed 
  

   (Asclepias 
  syriaca) 
  

  

  Photograph 
  hy 
  Jesse 
  L. 
  Smith 
  

  

  