﻿POLLINATION 
  AND 
  FEKTILIZATION 
  155 
  

  

  5. 
  Some 
  willows, 
  as 
  the 
  common 
  yellow 
  willow 
  (Salix 
  alba, 
  var. 
  vitel- 
  

   lina), 
  are 
  usually 
  represented 
  in 
  this 
  country 
  only 
  by 
  pistillate 
  trees. 
  

   Can 
  they 
  bear 
  seed? 
  Can 
  they 
  be 
  reproduced? 
  

  

  6. 
  Of 
  the 
  various 
  methods 
  by 
  which 
  self-pollination 
  is 
  rendered 
  diffi- 
  

   cult, 
  unisexual 
  flowers 
  borne 
  on 
  the 
  same 
  plant, 
  unisexual 
  flowers 
  

   borne 
  on 
  different 
  individuals, 
  dichogamy, 
  dimorphism, 
  which 
  is 
  the 
  

   least 
  effective? 
  Which 
  is 
  the 
  most 
  effective? 
  Give 
  as 
  many 
  instances 
  

   as 
  you 
  can 
  of 
  plants 
  which 
  exemplify 
  each 
  method 
  (not 
  citing 
  any 
  of 
  

   those 
  mentioned 
  in 
  this 
  chapter). 
  

  

  7. 
  Describe 
  as 
  well 
  as 
  you 
  can 
  the 
  qualifications 
  of 
  each 
  of 
  the 
  fol- 
  

   lowing 
  flowers 
  for 
  securing 
  pollination 
  : 
  hazel, 
  birch, 
  box 
  elder, 
  butter- 
  

   cup, 
  nasturtium, 
  horse-chestnut, 
  dandelion, 
  locust, 
  sweet 
  pea, 
  primrose. 
  

  

  8. 
  Ex 
  j 
  'lain 
  w 
  r 
  hy 
  the 
  subject 
  of 
  pollination 
  is 
  an 
  ecological 
  one. 
  Can 
  

   you 
  give 
  any 
  reasons 
  why 
  plant 
  ecology 
  is 
  one 
  of 
  the 
  most 
  difficult 
  

   divisions 
  of 
  the 
  science 
  of 
  botany 
  ? 
  

  

  9. 
  Give 
  some 
  practical 
  applications 
  of 
  the 
  principles 
  of 
  pollination 
  

   to 
  agriculture 
  and 
  horticulture. 
  

  

  