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  INTRODUCTION 
  TO 
  BOTANV 
  

  

  The 
  strong 
  odor 
  of 
  many 
  kinds 
  of 
  milkweed 
  flowers 
  and 
  

   the 
  abundance 
  of 
  nectar 
  which 
  they 
  afford 
  bring 
  them 
  main 
  

   insect 
  visitors. 
  On 
  the 
  Mowers 
  <f 
  one 
  common 
  milkweed 
  l 
  in 
  a 
  

   single 
  locality 
  one 
  hundred 
  fifteen 
  kinds 
  of 
  insect 
  visitors 
  have 
  

   been 
  found, 
  including 
  bees, 
  wasps, 
  ilies, 
  butterflies, 
  and 
  beetles.- 
  

   141. 
  Insects 
  as 
  carriers 
  of 
  pollen. 
  Most 
  flowers 
  which 
  re- 
  

   quire 
  or 
  are 
  benefited 
  by 
  cross-pollination, 
  and 
  which 
  are 
  not 
  

   wind-pollinated, 
  depend 
  upon 
  insects 
  as 
  pollen 
  carriers. 
  It 
  is 
  

  

  not 
  an 
  over-statement 
  to 
  say 
  that, 
  

   in 
  general, 
  flowers 
  seem 
  to 
  have 
  

   acquired 
  their 
  odors 
  and 
  their 
  colors 
  

   (other 
  than 
  green) 
  as 
  means 
  of 
  at- 
  

   tracting 
  insects 
  which 
  may 
  serve 
  to 
  

   cross-pollinate 
  them. 
  Insects 
  vary 
  

   greatly 
  in 
  their 
  efficiency 
  as 
  polli- 
  

   nators; 
  the 
  small 
  ones 
  with 
  smooth 
  

   surfaces 
  on 
  the 
  head, 
  legs, 
  and 
  abdo- 
  

   men 
  (such 
  as 
  ants 
  and 
  many 
  beetles) 
  

   carry 
  little 
  pollen, 
  while 
  bees, 
  moths, 
  

   and 
  butterflies 
  often 
  carry 
  considera- 
  

   ble 
  quantities. 
  As 
  already 
  suggested, 
  

   insects 
  are 
  led 
  to 
  visit 
  flowers 
  in 
  

   order 
  to 
  get 
  pollen 
  or 
  nectar. 
  Almost 
  

   any 
  insect 
  can 
  obtain 
  pollen 
  from 
  

   flowers 
  of 
  the 
  ordinary 
  type, 
  but 
  the 
  

   nectar 
  seekers 
  are 
  frequently 
  provided 
  with 
  a 
  very 
  long 
  sucking 
  

   tube, 
  or 
  proboscis. 
  The 
  honeybee 
  (fig. 
  130) 
  and 
  the 
  sphinx, 
  

   or 
  hawk, 
  moth 
  (fig. 
  131) 
  are 
  good 
  examples 
  of 
  nectar-sucking 
  

   insects 
  ; 
  and 
  the 
  sphinx, 
  with 
  its 
  slender 
  sucking 
  tube, 
  often 
  

   many 
  inches 
  in 
  length, 
  is 
  especially 
  well 
  equipped 
  for 
  getting 
  

   nectar 
  from 
  narrow 
  corolla, 
  tubes. 
  Cucumbers 
  grown 
  under 
  

   glass 
  afford 
  a 
  good 
  practical 
  illustration 
  of 
  the 
  importance 
  of 
  

   insect 
  visits; 
  it 
  is 
  found 
  necessary 
  to 
  keep 
  hives 
  of 
  bees 
  in 
  

   the 
  cucumber 
  houses 
  in 
  order 
  to 
  insure 
  pollination, 
  fertili- 
  

   zation, 
  and 
  consequent 
  crops 
  of 
  cucumbers. 
  

  

  1 
  Asdepias 
  verticillata. 
  

  

  FIG. 
  135. 
  Under 
  surface 
  of 
  

   body 
  of 
  a 
  bumblebee, 
  to 
  the 
  

   hairs 
  of 
  which 
  many 
  pollen 
  

   masses 
  of 
  green 
  milkweed 
  

   (Acerates) 
  are 
  clinging 
  

  

  After 
  Robertson 
  

  

  