﻿140 
  

  

  INTRODUCTION 
  TO 
  BOTANY 
  

  

  In 
  many 
  kinds 
  of 
  plants 
  self-pollination 
  is 
  entirely 
  effective. 
  

   In 
  others 
  it 
  produces 
  seed 
  which 
  is 
  good 
  but 
  not 
  so 
  abundant 
  

  

  or 
  so 
  sure 
  to 
  grow 
  into 
  vigorous 
  plants 
  as 
  

   that 
  which 
  is 
  due 
  to 
  cross-pollination. 
  In 
  

   still 
  other 
  plants 
  cross-pollination 
  is 
  abso- 
  

   lutely 
  essential 
  to 
  the 
  production 
  of 
  seeds 
  

   that 
  will 
  grow 
  at 
  all. 
  

  

  To 
  the 
  fact 
  that 
  self-pollination 
  is 
  in 
  

   many 
  cases 
  not 
  wholly 
  satisfactory, 
  but 
  

   better 
  than 
  none 
  at 
  all, 
  is 
  probably 
  due 
  

   the 
  existence 
  of 
  many 
  flowers 
  like 
  the 
  

   common 
  dooryard 
  mallow, 
  or 
  " 
  cheeses," 
  

   which 
  has 
  moderately 
  showy 
  petals 
  and 
  is 
  

   often 
  cross-pollinated 
  by 
  insects, 
  but 
  can 
  

   also 
  pollinate 
  itself 
  by 
  the 
  contact 
  of 
  the 
  

   curving 
  stigmas 
  with 
  the 
  stamens 
  (fig. 
  122). 
  

   Such 
  flowers 
  are 
  sometimes 
  able 
  to 
  secure 
  

   insect 
  pollination, 
  but 
  in 
  default 
  of 
  this 
  

   they 
  do 
  produce 
  a 
  crop 
  of 
  seeds 
  as 
  a 
  result 
  

   of 
  their 
  self-pollination. 
  

  

  133. 
  When 
  self-pollination 
  is 
  advantageous 
  ; 
  cleistogamous 
  

   flowers. 
  Some 
  flowers 
  are 
  usually 
  self 
  -pollinated 
  except 
  when 
  

   cross-pollinated 
  by 
  accident 
  

   or 
  human 
  agency. 
  Wheat 
  

   is 
  a 
  notable 
  instance 
  of 
  the 
  

   kind, 
  and 
  apparently 
  self- 
  

   pollination 
  can 
  go 
  on 
  in 
  

   this 
  grain 
  for 
  a 
  long 
  period 
  

   without 
  injury 
  to 
  the 
  fer- 
  

   tility 
  or 
  the 
  robustness 
  

   of 
  the 
  offspring. 
  1 
  Experi- 
  

   ments 
  in 
  raising 
  selected 
  

   varieties 
  of 
  tobacco 
  seem 
  

   to 
  show 
  that 
  in 
  this 
  plant 
  

  

  KM;. 
  \~2~1. 
  Stamens 
  

  

  and 
  pistilsnf 
  rmind- 
  

  

  k-aved 
  mallow 
  

  

  The 
  flower 
  has 
  heen 
  

   open 
  for 
  a 
  consider- 
  

   able 
  time, 
  and 
  the 
  

   stigmas 
  have 
  curved 
  

   so 
  as 
  to 
  touch 
  the 
  

   anthers 
  and 
  in 
  this 
  

   way 
  absolutely 
  to 
  in- 
  

   sure 
  self-pollination. 
  

   After 
  H.Miiller 
  

  

  FKI. 
  123. 
  Facilities 
  for 
  insect-pollination 
  

   or 
  self-pollination 
  in 
  flowers, 
  if 
  the 
  matri- 
  

   mony 
  vine 
  (Lycium) 
  

  

  In 
  the 
  flower 
  at 
  the 
  left 
  (earlier 
  stage) 
  the 
  

   anthers 
  are 
  spread 
  apart 
  and 
  are 
  likely 
  to 
  

   come 
  in 
  contact 
  with 
  insect 
  visitors; 
  in 
  the 
  

   Mower 
  at 
  the 
  right 
  (later 
  stage) 
  the 
  anthers 
  

   close 
  together 
  over 
  the 
  stigma, 
  insuring 
  

   self-pollination. 
  After 
  Knutli 
  

  

  1 
  See 
  "Wheat: 
  Varieties, 
  Breeding, 
  Cultivation," 
  Bulletin 
  62, 
  Univ. 
  of 
  

   Minn. 
  Agr. 
  Exp. 
  Sta., 
  1899. 
  

  

  